This is very weird. I know that if you have sight of view on all the map then a nest can spawn into your base.
But on big maps when there are tons of space where we don't have units/radar.
I'm talking for example of the map chicken nugget and comet catcher redux. We have the front where it should be, tons of room for chickens. 0 nest in our base and suddenly a white dragon spawn right in our back 1 cm from a singularity. It blows everything and we lose the game that we were doing great.
So no, I'm more than 100% sure we have no units covering the whole but only the front and our entire base.