After researching a bit, there are several definitions for drainsoul.
According to the wiki, the skill at level 60 deals 125 damage and heals the bloodmage for 93.75 health.
According to /skill drainsoul ? in game, the skill at level 60 deals 125 and heals the bloodmage for 96 health. (I am assuming this is the correct skill definition)
According to what is actually happening in game, the skill at level 60 deals 125 damage,
and heals for 68 health even though the heromod claims the heal is 73 hp. (Still wrong)
Could this be because the self heal reduction is actually reducing the amount of hp the skill gives back even though the hp couldn't be given to any other player?