I agree I think angle of attack has a lot to do with it.
Something that is guranteed to help you shallow your swing out is an aid to keep your left arm straight. You can buy one its a sleeve that goes over your leading arm elbow but seriously you can improvise by using a 2L coke bottle like I have done in the past. Cut both ends off and slide it onto your arm.
You should be able to hit full shots wearing it , your backswing will of course feel more restricted but that is not necessarily a bad thing. IMO a great way to cure over-swing and to get better extension into the downswing. Your shot trajectory will change a lot and definitely worth a try.
