Adrenaline, naa?
I was trying to find out if there is actually a formula in the game engine that calculates this or if it is just a tabulated thing.
Personally, I suspect that there's some formula involved that involves square roots and ceilings. (For instance, note that 3, 8, and 15 are respectively (2^2) - 1, (3^2) - 1, and (4^2) - 1.)
I don't have the requisite skills to peek into the game's codes, though :/