Well, I'm just going to go out on a very solid limb here and say that since I've already answered that question and have known the answer since the first week I hopped in a tank, my head is in no danger of exploding from reading him ponder the implications of either answer.
And W'maker, I'm not sure what you DO mean by this: "My point was that even if the tank wasn't buttoned up, you'd have a commander in the cupola looking out and even if not, it would still be impossible for the gunner to aim and look out of the cupola at the same time."
You can't be in both the commander's cupola and aiming the gun at the same time. Based on your post, I thought you were confused as to wether we have a little cartoon driver scrambling from position to position, or wether we simply jump into that crewman's body so we can control his actions. Tell me if I'm hitting any where in the ballpark with this.