I was under the impression that, in pistol shooting, the larger the caliber, the more difficult it is to shoot; therefore, it's fair that the bigger caliber guns have larger scoring areas. In centerfire pistol matches there's often a trade off, do you select an easier shooting .32, or a .38 with its bigger hole?
On the other hand, you're shooting at a pretty close range, I've never shot at anything that close, but I've never wintered-over in Canada. If your targets are only 8 to 10 feet away, it seems the guys with the longest arms have the greatest advantage.