It depends a bit, where you're looking:
4 => 5 : 0.23%
39 => 40 : 0.22%
For level 96 it's 29%, for level 1 it's 4.87%. That is an increase of 24.13%, or 0.25% on average per level. Anyway, like with the ToR you have to level up your AO by more and more levels to gain a significant...