Spawning in Specific Areas

Ultimately, you need to define "some point" within "some space". For example, you could spawn units within a sphere centered around the player. You could place a series of trigger colliders, then use their bounds values to pick a random point within a particular box.

It sounds like you're after something closer to the trigger-colliders method. The player could keep track of which trigger(s) they're currently in, then you just need to pick a random point within those volumes.