As I didn't see it here anywhere before, let me put this up.
How bonus works:
Bonus value base: # of achievements completed
+1/wave (in level)
This is if I recall correctly.
So, very beginning of ever playing the game.. you'll only get bonus of 100 at end of the level.
The bonus is added to the kill of EACH unit. (don't recall the actual value per unit, but it varies depending on unit...
maybe I'll check sometime to see.
also, to just reset everything in your game to start.. delete the .bak file off your phone.