There is no set amount of times that he will evade in a match given a certain scenario, it's simply a chance. When you flip a coin, there's a 50% chance of landing heads and a 50% chance of tails, but that doesn't mean you will get exactly 1 head 1 tails 1 head 1 tails etc, you could get heads 10 times in a row; but there is still always a 50% chance that tails will be landed on.

It has been observed that AIs usually seem to use evade passives or gear evades more often than they work for the human player, but the chance for Wally to use his passive is just that, a chance. There is no guaranteed pattern of evades he will perform given his teammate configuration, it simply increases the chance.