Lashes of the slave

Noticed that the calculation as to how many mv % you lose is done before the damage is dished out. This is a bit unfair sometimes: I was fighting mob that was convulsing. I executed lashes of the slave, and it died on the first lash. However, I lost 15% of my mv%, whereas I should lose 3-5% typically for a one-lash Lashes of the slave. This probably means that I "suceeded" in dishing out multiple lashes, but since the mob died on the first one, I spent 10% of movement points. This probably sounds anal, but since this skill is hard to perfect and costs a lot of movement points, every little bit helps.