Screw won't help if it isn't getting stuck.
It sounds like your problem is the mech isn't level. Think about it - Coin mech is at a right angle to the coin door. Playfield is at a 6 1/2 degree pitch. Whole game is at a 6 1/2 degree pitch. So your mech is leaning to the coin return side.
Put your mech on a level surface and see if coin goes to return or the coin switch side. If it works on the level surface, then you need to find different mechs that will work or get your mechs leaning back the other way.
Been a problem with pinball since they started mounting the mechs in this fashion.
Stern is the only one to recently rout out more wood and lean the whole door in a bit.