That's not the only place where zombies can spawn in sight. When I cleared the Navezgane County Jail, I had soldiers spawn within arm's reach when I was outside. I'd jumped up on the small roofed area in the yard, and when I jumped down, zombies spawned right on top of me.
Basically, it would be nice if they could force zombies to spawn outside of sight, but that's never really been the case. I remember sitting on top of my base on horde nights watching zombies stand up from spawning in and seeing if I could kill them with arrows before they took their first step after standing up (this was likely back in A16, though...vultures have stopped me from doing this.)