Hey.

Villain opens from BU 40%. It is something like this: (in my opinion). We are on BB.

.1...Villain has 20BB stack. Probably in this situation doesnt make sense to have calling range. Our play is fold/shove.
How do I calculate what will be profitable to get in? I have no idea. On internet I can find some shoving ranges but I can not find WHY the ranges.
I would like to understand logic / mathematics.

.2...Villain has 40BB stack. In this situation we want to have calling range (probably).
What changes if the stacks are slightly bigger?

BTW: Does it make sense for villain to open so wide range if he is shortstack?
Thank you very much!