Well, if we ignore dispersion for a moment, taking a worst-case scenario of 150 yards convergence, at 300 yards the bullets would be spread back to 19 inches, correct? Then for every 150 yards out it would widen by another 19 inches.
So going over a space of 850 yards from convergence, I get 5 2/3 * 19 inches, so 107 inches. Or about 9 feet.
So it's not negligible if you consider the worst case we can give it in game. Myself, I set it to 650 and go on about my day because at that convergence setting its effect is practically irrelevant compared to dispersion.
Wiley.