So, 2x Energy, 2x explosive shot, 2x 9 shot. I died because I accidentally went down to 1 energy while no paying attention. I think the difficulty should ramp up more, because nothing was getting away from the edge of the screen.
Quite a good combination indeed. I found out that the single bomb sometimes helps, you can use it quickly to get rid of some frontrunners before setting up a new explosive barrage.