I have noticed same wierd dispersion..
Once strafed tower, but I barely hit it even from 200-100 yards, and I saw bullet hits on it's right side with about +15 degrees from center point. (my convergence was 300)
Can't believe it was because of dispersion..
Though, I experienced this same with P-38 also, saw bullets hit 15-20 degrees right from centerpoint from distance of 100-200 yards.