Stats for that mission show 45 shots fired, 36 shots impacted. Do not fire during the introductory zoom – all shots fired before wave 1 starts are still counted as part of wave 1.
I can’t control that per-difficulty. But I’ve reduced it. 
Idea
Hend Game always stops the music no matter what. Other bosses have more complicated rules, depending on whether the stage ended, and/or the upcoming music is different than the current one. It’s not important enough for me to waste time on it.
75%
100%