I would partially agree. There were several viewports on most tanks and yes, your visibility is more limited than an infantryman’s on foot. But, I think a squad sneaking up on a vehicle from the front is questionable. More than likely, they would be spotted and shot to pieces. I’ve read many books on WWII and have never read an account of infantry “sneaking up” on an armored vehicle from the front. It was always done from the sides or rear and even then not very often. If they did, there was lots of cover, like in a town. That said, for game purposes, a squad sneaking up from behind would be more feasible. Thus, no defensive fire in the vehicles rear hexes makes more sense, than none at all.
-Magoo