My pet theory is that the solver is manipulating the stack depth to limit the power of your opponent's 4-bet. I call this the Efficient Jam Principle - solvers will fight to limit the power of each other's shoves, and maximize the power of their own shoves.
100bb deep, BTN 2.5bb, BB makes it 13bb
BTN wants to 4-bet, they can't do that effectively vs this size. They have three awkward options:
- 4-bet to around 26bb, putting in a flaccid half-pot raise with a polarized range.
- 4-bet using a more natural pot-sized raise to 39bb, then being forced to drastically over-defend vs a shove
- 4-bet shove 330% pot
Exploring shorter stack depths, you see a similar pattern, where BB will 3-bet in such a way that the opponent has to choose between a min-click 4-bet or a shove.
Exploring deeper stack depths, you see the IP raiser using a more natural pot-sized 4-bet, e.g. at 200bb the line might look like this: 2.5bb -> 12bb -> 38bb
I explore this theory a bit more in my
preflop mechanics video.