Something I stumbled upon recently is that when I'm looking through GTO wizard's preflop ranges, it seems like the BB is actually defending a wider range of hands vs. early position raises than when facing a raise out of LP. Below you some of the ranges and defence frequencies. As you can see, BB is defending more vs. MP than vs. CO/BU opens.

I'm wondering why this is, as intuitively you would expect BB to defend wider vs. a weaker opening range. My hunch is that it's a consequence of MP using a smaller opening size.

1. This simply offers better odds for a call and BB needs to win the pot less often postflop to call profitably.

2. Smaller sizes lead to lower SPRs which improves equity realization for all the medium/low suited hands that find a call vs. a smaller sizing. Although this hand class should in general be underrealizing oop, with an SPR implied by a 2bb open they can realize their EQ better than with an SPR as implied by a 2.3/2.5bb open.

Any thoughts on this?

BB defence vs 2bb MP open (continuing 43.5%)

BB defence vs 2.3bb CO open (continuing 36.3%)

BB defence vs 2.5bb BU open (continuing 39.1%)