Besides what others said that lowering fumbles has made it worse for you (it's an inverse slider), make sure when you use R1/RB that you keep holding it until the tackle/contact is over. You don't want to just hold it for the initial hit and then let it go - hold on to it until they bring you down or you aren't getting touched by that player anymore. If you just use it for the initial hit, they can still force a fumble by trying to strip the ball while dragging you to the ground.