This is dead wrong . It does do more damage from the more focus spent . Easy test to do is to take all trinkets off and unspec all talents that increase damge(for example the stacking ap buff) and compare 100 focus head shots to 20 focus head shots and you will see 100 focus headshots do about 17% more damage (non crits).With that said as of now it's better to use at low focus becuz 17% ish more damage isn't worth 80 more focus. This could change numbers wise ofc. Anyway my guess is you are seeing the same numbers from 20 and max headshots becuz of talents buffing the damage or something. Go try what I say and try to dispute, but 100 focus head shot does scale with focus on alpha, it's just not worth it atm