LP System in 3v3

So my buddy and I play 3v3 ranked, im silver hes platinum. For some reason i get matched with other silvers and when i win i get 13 lp and lose almost 25. Same thing with my friend who is platinum his league name is Heroboner, gets matched with masters and challengers in 3v3 and he loses 28 lp and they gain 40 lp. Riot fix this system it makes no sense