@AIRB0RNE6176 You are correct, on a full length barrel and the MI rail you would need the extra 4" to get your light flush or close to flush with the muzzle. If you were still interested in the rail you could use a T.REX Lightbar Scout Mount which is 4.5" long. That would definitely get your light setup flush or as close to flush with the muzzle.
https://www.trex-arms.com/store/Lightbar-Scout-Mount/