Tri-rail question

When mounting a Hawke bubble level on to the Airforce tri-rail, I noticed that it doesn’t lay snug with the base of the rail (its only hold on with the clamps and screw on the side). I the mounted it on the dove tail below and it fit snug (no more looking through under it). I noticed the same with the scope ring mount (also Hawke), I can look through the bottom of the scope ring mounts. Is this a machining error on the tri-rail, scope rings? Does the base of the the scope rings and bubble level have to be lay snug on the tri-rail?