I see what you're getting at, but I don't think a sniper could have such a good portion of the map covered. It's hard to judge without having a picture of the maps and special ammo locations, but in general the best sniping spots don't have a good vantage point on both ammo and a large portion of the map. For example, consider the map First Light, which was by far the best map for sniping in the Beta- there were special ammo crates in the doorway near A; on the floor of the large dome room connected to A; on the ridge directly across from the dome headed towards C; (I think) in one of the tunnels on the outskirts of the A to C path; a little ways behind the turret at B; and at the base of the large wall next to the hollow tubes. There are probably one or two more, can't remember right now. Given those locations, the only places a sniper could set up shop and possibly have good visibility of both an ammo spawn and a large portion of the map is on the very top of the building at B (L.O.S. on the ammo closest to C) or right behind B towards the edge of the map (L.O.S. on the ammo near the hollow tubes). The caveat to those is that they're in one of the most contested parts of the map that players can get a good shots at from many directions, making it likely that the sniper won't last long. But for the other spots the sniper would still need to move to get the ammo, just not run straight up to it. They're still in danger, but less so than normal.