NRA B16 SF target bull is 5.3"....pretty close to the six that you supposed. If you want to win....you must be shooting the nine and ten ring ...2.6".
There is something to be said, also, about the mindset/ philosophy that underlies different competitions. Bullseye shooting is, as I see it, a sporting event. Combat shooting at human silhouettes or photo posters is substantially different.....otherwise the targets would be round bulls or simple poppers.
Not better or worse....different.
"Only hunting and mountain climbing are sports. The rest are just games." - R.Ruark
NRA Life Member