At least for melee, if you hold down the attack button for 0.6 seconds after your attack animation hits the "ready" position, your damage peaks at 150% damage, then plummets quickly the longer you hold it, down to 120%. This may or may not apply for range and thrown, I dunno.
Also keep in kind that the speed of your target will also effect damage to a small extent, so if he changes directions a smidgen or such.
I am sure there are also other variables at work.