How to change HP Drain Value

I am trying to make a holy spell for the damage dealing class that when it deals damage to enemies the spell will heal the caster 50% of the damage that the spell inflicted on the enemy but I noticed that it gives the caster 100% of heals to the caster, is there a way to change the damage type's HP Drain value?

You have 2 options:

1. Scripts like Yanfly's Convert Damage. Or make your own version in the Game_Battler.

2. Damage Formula: Make the damage be HP damage. With a formula like this:

     c = damage_formula; a.hp += (c / 2).to_i; c

Nope the script doesn't work with MogHunter's battle engine.

I figured doing the damage formula would be a easy solution without the script, the spells damage formula has this layout.

a.mat * 7 - b.mdf * 2

With the HP Drain type, how to change the damage formula that it can drain only 50% from the damage it inflicted to HP?

You can't change the % drained when the attack type is HP Drain.

You have to change the damage type to HP Damage and use something similar to the formula I mentioned above.