Punishment curse / Overkill damage with Culling strike question

Hey mates!
Question here I'm trying to figure out,
Using punishment curse , 10% of overkill damage is reflected to other enemies so my question is where I also have culling strike.

When culling strike does the killing hit is there any overkill to reflect?

Cheers!

No. Culling basically deletes the remaining health on mobs and kills them instantly. There is no overkill there. You'll still get overkill as usual when you do enough damage to kill mobs outright, as that will prevent a cull from occurring, but when culls do occur they won't interact with your Punishment.