Can enemies spawn outside of the spawn circle?

I have now finished two sectors, and my tactic on both has been to block their way and lead them to one place where i can blast the frick out of them. This has worked flawlessly on both sectors, but today i moved on to the third sector which i have called "99 Problems". I used the same tactic for this sector. Block, lead, trap and destroy! But this time, the enemies seem to spawn way outside of the spawn circle which has me frustrated. Is this possible? Or is it just me who havent found the second spawn circle?