Question about xp penalty for lvl difference

[knightawc 85]

I know if I go killer with a high lvl to a new map I get a penalty on the xp (instead of receive the 100% of the xp from each mob I will gain less).

Now the question is, when I go with a leecher, he also get that penalty?

After all he isnt who is killing the mobs, thats why my doubt.