EXP confusion

So I'm playing in a party with some friends in co-op vs ai and my friends keep getting obscene amounts of exp compared to me. Example: they have 230 while i have like 90.

I just don't understand how they can get so much more when i have so much more kills or Because they kill monsters, i tried that too. Ive tried different champions different lanes. i even tried making someone else leader of the party just in case that was doing it.

This frustrating because i don't know why even if i knew why and still couldn't get it id understand, sorry i ranted a little, anyways thanks for the help.