Scaling Opinions? Help Needed.

Sorry for asking so many questions, but I just need your guys's opinion on sizing.

I am fitting a destiny helmet to a model of my head that I created. However, after fitting it to the height of my head, I found that there was a ton of extra space in the back. Any opinions on how I should size this?

The black line is where the visor is, and the white lines are the hole in the bottom.

in my opinion its okay . my warlock helmet are like that too . as long it fits and proportional scaled . the new helmet im working on , HezenLord is like that too . freaking long to the back.