Jam/Fold: Optimal versus Exploitive play

[indianaV8]

The problem is: You are on the SB (blinds are 1/2), stacks are let's say 16 after the blinds are posted. Only jam (push allin), fold, and calls are allowed. The optimal play for this setup is 58% (hand range) jam, 39% for the caller. Now the thing is, that you know that your opponent is calling 20% on average when you push.

Question 1: Can you assume that 20% fixed call range brings same EV as 20% "you get a call on average", i.e.:
a) Your opponent will call with top 20% hands
b) Your opponent will call 20% of the time: i.e. if you push 1m times, 200k times you'll get a call. (so you may be against a rock for the next 500k games that will call with 2% and then against fish that will call with 40%)
Are a) and b) equivallent?

Question 2: By adjusting your range to the optimal jam range versus 20% call range does your EV increase (considering Q1 is answered 'yes', the answer here is obviously yes, and if not ... eventually not so obvious).

Question 3: If you play optimal exploitive range (against the 20% caller) is it alays the case that the EV from this is better than if you choose any other strategy between the optimal exploitive jam range and the optimal range versus any caller (remarks similar to Q2).