First, i have to have both daggers with vampiric (nowhere to put swift or +dmg unless i find an ultra rare vampiric+swift combined enchancement) to have the most possible lifesteal

Second, even after that i am still lifestealing a very little amount because the further into the game the more damage in attack comes from modifiers like heroism or might breakpoints or skill modifiers.

Or does skill count?

I mean, if i have a dagger with 2d3+6 (8-12 dmg) and i have my total damage from attack equal to 17-21 because of other effects, will i gain 8-12 hitpoints when i hit or 17-21?

From what it seems when i actually try it, its even less than both those values.... Do i only gain 1/3 of the life back, like vampire's first spell?