LBE – minimal balance changes for Heroes V 3.1.

I think it would be good to reduce the Drain Life ability of the Vampires even further.

Nah, why? - If they are unbalanced, you can reduce their stats (for example, attack - then their damage will be less, and as a result, their self-healing will be reduced).
If we make it like in Heroes 6 (where it's about 20%), it will be a very weak ability - just my opinion.