I checked all my barrels with scopes and as you say there is a little air or light under every one of them kinda like hanging out in thin air but the scope is solid from where the screws are to the back of receiver and I have never had one shoot loose. I picked up a stainless barrel the other day, TC custom shop barrel with matching silver base and it is the same way. I think there have been some post on this before. I also checked one of my bbl barrels and there is a little light under it but not as much.
Deaconllb