Adjusting to Different Open Sizes

One of the most common leaks in micro-stakes tournaments happens in the Big Blind. Many players either defend too wide regardless of the raise size or over-adjust and fold too much. The key to mastering Big Blind defense is understanding how Raise First In (RFI) sizes affect optimal strategy.

In this guide we’ll break down how to construct your Big Blind defending range against different open sizes and explain how to adapt to the tendencies commonly seen in micro-stakes games.

Common Mistakes in Micro Stakes

Many micro-stakes players misunderstand how sizing influences ranges. This usually leads to two major mistakes:

1. Static Big Blind Defense

Some players defend the same range regardless of open size. They ignore the price they are getting and the likelihood that the opener’s range changes with larger bets.

2. Over-adjustment

Others go too far in the opposite direction. When facing a bigger raise they either:

• Under-defend and fold profitable hands, or
• Over-defend with weak hands against a stronger, often polarized range.

The goal is not to abandon your strategy, but recalibrate it based on the conditions.

The Scenario : A Simple Tournament Toy Game

We examine a Button and Big Blind each at 35bb, as part of an equal stack 35BB model.

The model makes use of four strategic options for the Big Blind; Fold, Call, raise 3.3x (the Big Blind RFI) and all-in.

In a chip EV (cEV) environment the button generally should open to a size around 2.2bb at 35Bbb, opening 47.5% of the time. Other Raise First In sizes that are similar are equally appropriate as we will explore later. I.e. we would not expect significant strategy changes if our opponent makes it 2.1bb instead of 2.2bb.

Naturally as the In Position player selects a larger Raise First In Size, the amount of hands the Button can open profitability decreases to 39.9%.

While it’s important to learn GTO preflop ranges for each position in order to understand the theoretical baseline, it’s equally important to recognise that most players in micro-stakes tournaments are not playing these ranges. The majority of the player pool is recreational and playing primarily for enjoyment, which means their decisions are rarely based on balanced strategies.

As a result, although the models used in this article show balanced, equilibrium ranges for different RFI sizes, the reality at micro stakes is often quite different. Many players are not opening a wide, well-constructed range. Instead, their raises are frequently value-driven and heavily weighted toward stronger hands.

Even when we suspect this is the case, it doesn’t mean we should automatically fold every marginal hand in the Big Blind. The Big Blind still benefits from strong pot odds and implied odds, especially when holding hands that can realise equity well in postflop situations.

However, the key is balance. We want to avoid the common mistake of over-defending, where we continue with too many weak hands simply because we are getting a price. Consistently calling with marginal holdings against ranges that are stronger than expected will gradually bleed chips over time. The goal is to defend profitably—taking advantage of the odds when appropriate, while avoiding the trap of putting additional chips into the pot with hands that struggle to perform in the postflop game tree.

Defending vs a 2BB Open

A 2BB open is typically used at very short stack depths (around 25BB or less).

Because the Big Blind has already posted 1BB, calling a min-raise requires very little additional investment. This gives the Big Blind excellent pot odds, allowing for a very wide defense.

Key adjustments:

• Defend extremely wide
• Defend any Ax Kx Qx vs steal positions
• Mix in polarized 3-bets

Polarised Big Blind Raises

When raising from the Big Blind at standard stack depths, theory suggests a polarised strategy. This concept is often referred to as blocker-based duplication in range construction.

• Value hands; strong hands that dominate the opponents calling range and want to build the pot pre-flop (e.g. AA, KK, QQ, AK)
• Offset bluffs; that duplicate our value, block our opponents value and unblock folds at the bottom of their opening range (e.g. 3bet bluffing A3o, J7o, T7o make IP fold A5o, J8o, T9o)

Defending vs 2.2BB ‘GTO’ Opens

At around 35BB stack depth, a 2.2BB open is generally considered optimal.

From a practical standpoint, players should treat 2.1BB–2.3BB as essentially the same size. Population tendencies often dictate these differences rather than strategy. In reality the expected value and pot odds are virtually unchanged by such smaller variations in sizing.

For example:

• One player may always click 2.1BB
• Another may default to 2.3BB

But both might be opening identical ranges, so avoid over-adjusting to tiny sizing differences. Treat these sizes as standard opens and defend using your normal Big Blind strategy relative to the position and the effective stack depth on the table.

Defending vs 2.5BB Opens

When open sizes begin to creep above 2.3BB, especially in micro stakes, this often indicates a stronger opening range.Many recreational players instinctively increase their raise size with stronger hands. This is often referred to as ‘betting what their hand is worth’

Because of this:

• In theoretical models, we see 3-bet frequency drop compared to smaller opens. E.g. Big Blind 3bets 8.5% non all-in at 35bb vs 2.5bb raise first in, compared to 10.1% at 35bb vs 2bb raise first in.
• The Big Blind should tighten its off suite calling range in particular, calling 51.6% of range
• And more focus should be placed on hands that perform well postflop, hence suited hands remain fully resilient even against the increased raise size

Defending vs Inappropriate Opens Sizes

Once the open size reaches 3BB, the strategy at short stack depths dynamic shifts again and largely can be described as no longer optimal given the stack to pot ratio.

The Button is investing more chips into the pot, which creates a larger pot to fight for.

This has two key effects for the Big Blind:

1. Calling becomes worse, reducing to 33.7%
2. Raising becomes more attractive, 6.9% non all-in and 11.9% all-in

Hands that were previously comfortable calls (like Q8o, J8o, T8o) begin to fall out of the defending range. Instead, the Big Blind strategy shifts toward 3-betting for value with less bluffs in the range overall.

Tournament Considerations: ICM and Bubble Factor

Everything discussed so far assumes a chip EV environment.

As tournaments progress, ICM pressure and bubble factors change the incentives dramatically.

Under ICM:

• Calling becomes worse
• Aggressive actions increase
• 3-betting becomes more common

This further reinforces the idea that passive Big Blind defense becomes less attractive later in tournaments.

Key Takeaways

Always consider the opponent’s open size, your Big Blind defence should change depending on how large the raise is.

Defend wider versus smaller opens; Min-raises give you excellent pot odds and allow you to continue with more hands.

Don’t overreact to small sizing differences; Treat 2.1BB–2.3BB as standard opens.

Tighten against larger opens; When players raise 2.5BB or more, they often represent stronger ranges in micro stakes.

Adjust your 3-bet strategy; Against stronger ranges, 3-bet more linearly and bluff less.

Consider stack depth; Always think about stack-to-pot ratio (SPR) and whether the raise size makes sense for the effective stacks.