just for clarification, in YOUR statement, "I haven't seen any proof that engine-off makes any difference" you are meaning in an AIRCRAFT? Since you mentioned except in listening AC. Correct, AC's engine on or off has no effect on Vehicle Icon ranges,to my experience. You may however be able to HEAR a motor or track sounds,with AC motor off-IF close enough and slow enough so as not to get WIND NOISE in AC. I have heard of other GVers turning up "others engine" sounds and turning down "own engine"sounds to hear enemy GVs, but has no effect on ICON ranges As I understand it,with vehicles, ENGINE ON is treated as MOVING as far as Icon ranges go.