Been doing the math for the last 99 hand example. I think this is a reasonable short cut to figuring out how often we need a fold.

If I assume that 99 will have around 33% vs his calling range to a shove, then he has on avg 67%.

The difference between our equity is 34%.

Percentage we need a fold =

[(difference between our equity)*(effective stacks)- (amount lost if we fold)] / [(difference between our equity)*(effective stacks) + (amount of his 4bet)]

In this case:

=[(.34)*($572)-($32)]/[(.34)*($572) + ($80)]
=59.1%

We need him to 4bet fold 59.1% in the above example to shove 99. That seems pretty high to me, though I suppose its possible.

not sure if that short cut to an equation is helpful. Seems easier to me than writing it all out. In that equation, 'amount lost if we fold', includes the amount we 3betted and will be folding as well as any dead money. So in this example I should probably also add the $4 blinds (so $36 instead of $32 for accuracy)