Your observation makes sense because the bulk of the little time I spent balancing it was actually with fewer circles in place. I initially had two fewer circles, but I added a couple to sort of act as practice for the player, extend the play time a bit, and to make it look nicer.
If I had more time, I was planning to add a bonus circle for every 20 or so enemies that you kill. The game still plays well with about 2-3 circles more than what you see now. Anything above that and I’d have to re-jigger the distance between them to avoid it getting too cramped on the screen.
I finally topped my previous score and got 56, by the way.