Now after playing some more i still cant beat the level 35-40. Usually these type of games the enemies move around and shoot at the player, so not as many enemies needed. But since all your enemies are suicidal you make it even by adding more enemies. Eventually, where i always die, no matter what upgrades i choose i get overrun. There simply is way too many enemies!
How i usually have to play towards the end is hiding in either top or bottom of the screen cause yea too many enemies to even try flying around the given area.
Increasing the amount of hp on enemies is really acceptable. But also increasing the amount of enemies with the amount you do, it doesnt work. Either more enemies or more hp. Its like the amount of hp you increase times 3.
Can i ask if you have finished the game?