This game is pretty brutal. By the time I got to wave 6 I was far behind enough that the next wave spawned before I could kill the first one. That was the point I knew I had lost the run.
But the problem is that the monsters are too easy to kite. I flew around them in circles and kept them from killing my base for another 3 waves. And I probably could have kept going longer but I got bored and just let them kill it.
If you're going to make it so hard to defend at least make losing faster so we can do another run quickly.