If you are " gun barreling" you are not really gapping. You need to either lower your anchor point so that gapping works in the way you are shooting, or (likely best) do as B Ferguson stated and experiment to find YOUR actual gap.
If you have your arrow way up your cheek, your gap is gonna be very small. Note, however, that by doing that, your point on will be relatively close and farther than that your gap will be above the target.
Put a small target (stick on circle, anything) on the upper portion of your backstop, then put another smaller target 18 or so inches below it.
Use your gap aiming at the lower one and see how it hits the upper one (the actual target). If you are too low, raise the lower one, if it is too right, move it left etc until you have established a lower aiming point that allows you to hit the "target".
Once there, you have your gap (for that distance, from the ground). Now shoot some and enjoy. Then move closer and farther and see how that affects your gap.
Gaps change depending upon distance, however there is usually more of a gap range (like, maybe, 18" to 6" or some such).
Whether you focus on the point, or the target, or the gap target is gonna be completely whatever works best for you after you've been shooting a while. but give it a chance if you expect to excel.
CHuckC