the 20mm M197 mounted on the AH99 blackfoot and the 30mm 2a42 mounted on the Mi48 Kajman should have a greater round dispertion.
currently even if you shot at +1500m range all the rounds hit under 2m CEP which is not realistic and not effective when engaging infantry since there is no area saturation effect.
also the blast radius of HE rounds seems very low. one 20mm hit at one meter from an infantry unit fails to kill or even injure him.
real HE rounds kill radius : 20mm=2m (20x102), 30mm=3m (30x113, 30x165), 40mm=5m (CTWS).
injuries radius is generally twice the kill radius.