It all depends on what admissions is looking for. If you are in a big school, that school might offer you a lot more opportunities to engage in many different activities that will impress the board. In a small school with little to do, you can also get to do things that aren't part of the school, but to say one or the other will give you an advantage, I don't think they admission really cares. Plus attending a school next to military installation will not in any way affect the outcome of your application and remember that there are some kids that live and attend schools on military bases, and some of their parents are high ranking officers. Many of whom still don't end up receiving appointments, even with the military history and connections in their families. vGood luck!!