Ordering the correct size Shore Trooper Helmet

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Hey Troopers, I am ordering a Shore helmet from 850 armory works and I want to order the correct size from the jump. The circumference of my brow is 23 inches exactly and the bucket comes with no padding. My question is should I add an inch or 2 inches? I want it to have the extra room for the padding and fans etc, but not too big that I look like a bobble head. Any advice would be helpful so I dont have it made to big or small. 850 Armory is letting me make payments so I have a little time to figure out the proper sizing.

     I am a Shadow Scout Trooper(first build)SKG Pgh PA,  and when I got that helmet from Cybercraft it was loose and after installing my fan, voice mod, USB power stick, etc now it fits perfect. Any advice from a Shore would be a big help. I would hate to have to send it back and have them start all over again. I know from reading pathfinders posts that when putting on the helmet it is tightest around the brow and then opens back up once the bucket is all the way on. 

     Any advice would be greatly appreciated.  Best regards, Kenny Weber