Yeah balancing the rate at which fuel disappeared was a little tricky. Initially they did stick around for longer, but the problem was it made the dash less useful since there was ample time to kill all the enemies and then collect it before the next ones spawn, so I decreased it from 10s to 7s. I should have revisited it though because after that I updated the spawning script to double the rate at which the director gained credits (spent on enemy spawns) when there are no enemies active.