The reason AKs makes less of a difference when up against QQ is that some of the time you make a flush with AKs you would have won by making a pair anyway, so those boards dont contribute any extra equity compared with AKo. Vs AA its much less likely when you make a flush you would have won anyway, so the suitedness of AK adds more equity.

We can show this with a simple calculation

the chance of hitting a flush is ~5% higher with suited cards which means suited AKs adds roughly 5% equity vs AA. Against QQ we need to take away all the times we hit a flush but also hit an A or K with the other two cards. Given a board that is

xx there is 1-(41/47)*(40/46) ~ 25% chance that at least one of the two other cards is an A or K. So the equity added vs QQ is roughly 0.75*5% ~ 4%.

To do it properly we need a much bigger calculation since we need to take straights and stuff into account, but thats what the equilator is for ^^