So you say he has 20% 3bet (samplesize? not for handcount - I'm talking of the effective NUMBER of 3bets!). Concerning the concrete range of "20%" your A7s has 43 - 47% EQ depending on how you actually define those 20%.

Let's solve it by equity.

46% (your EQ) * 81.9$ (money you win) - 3$ (Rake) = 34.67$

54% (his EQ) * 69.9$ (your effective stack) = 37.7$

34.67$ - 37.3$ = -2.63$

With this equity calculation you loose sth. like 1 SB in each spot that you play here, so it's a really close fold (because of the rake!). All in all this may be a break-even spot regarding to the fact HOW you define his handrange, wether there are more low Aces included (that you have dominated) or more suited connectors (JTs, 98s etc.) where you have sth. like 35 - 40% EQ.

Last but not least I don't think there is a "perfect" solution because it all comes down to (1) samplesize and (2) the definition of the 20%. Depends on how much you like variance

best regards,

AK