I think if you drive right up to a PIAT squad the near accuracy should track. Currently circle strafe and you've got PIATs defeated.
I think this is a fair compromise. As I do agree with Doggy that you can't make them too accurate or else they would absolutely rape Mediums and Heavies. Not sure this is feasible programming wise but I'd settle for a munitions ability that any PIAT equipped squad could fire an "Aimed Shot" that either tracks or has better Accuracy.