So no firefly ever fired a single HE round in combat in WWII?
And it isn't true that most P-51's that lift with ordnance take 2 1000lb bombs and 6 HVAR rockets?
Also, the M4A3(76)W carried HE rounds, and used them in combat. The fact that some units complained about the decreased HE performance compared to the standard M4's proves as much.
Gunsight and trajectory for the 75mm Gun M3 are correct, or very close. For both rounds, mind you. The HE round would not under any circumstances have the same trajectory as the AP rounds, either M72, M61, or M61A1. The HE round had a different mass, and a lower muzzle velocity. Even one of those would result in a different trajectory from the AP round, and both could result in a significant difference.
However, since you seem to know it is incorrect, you may wish to share this information with HTC.