So I have a fairly standard M4 with a folding tube stock. I currently have a 4-16x50 Vortex mounted on the flattop. However, I cannot get a good sight picture due to the rings being too low. Can I get some suggestions as to what height I need. This is not my primary rifle so I don't want to spend a ton of money but I do want something that will do the trick. Thanks in advance.