With the saddle it doesn't appear slip and slide on him but it I have checked under the flaps (not with it done up i'll have to look at that). It doesn't appear to pinch his withers or anything. It doesn't sit along his back if that makes sense. At one point I did question it being a bit too narrow but I asked someone more experienced and they said the saddle was fine for him. So I'm not sure about that.
His bridle fits him fine just to be on the safe side I check it everytime. I don't think his bit pinches him but i'll check that when I go out with him next.