Well, the fraction after the call is the only ratio that matters. If you can't see the statistical reason for this.. maybe I can advise you to take your calculations with a grain of salt. (no offense here, but it's rather dangerous if you start basing strategies on your math when it's possibly flawed)

Now, if he will call with AA,KK,QQ,AK, and we know that the odds to get AK are equal to the odds to get AA/KK/QQ, then in 50% of the cases you have a cointoss to win, and in 50% of the other cases you are dominated.

Add to that the fact that unless you hit your set on the flop, you don't really know where you stand. (the reason that 22 vs AK is a cointoss is mostly that you win when they hit nothing.. and a little bit b/c of the fact that you win when they hit and you get a set.. but without seeing their cards it's kinda hard to gauge whether they hit something or not when the flop gives like a Q) So then basically what this boils down to is.. set-hunting with a low pp, what everyone does.