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 Defence

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.

Below we can observe the shift in frequency for an open to 3x. The amount of hands the Button can open profitability to a larger size 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 recognize 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 realize equity well in post flop 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 post flop 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 defence.

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.