Let's start off with a little background on how GS is calculated.
After 1.4, they started calculating PvE or Light Zone (LZ) GS (what you see on your character screen) and PvP DZ GS (hidden to players) differently. Before 1.4, cheaters would max out their gear and equip a secondary and sidearm with super low GS so they could artificially lower their GS to get into lower GS DZ brackets to grief players.
In order to fix this, the following changes were made to how GS is calculated, these weren't published by Massive but the community figured it out. Also, you'll notice that the calculations use the old weapon and gear item max scores, I didn't change these (pulled from an old post) to better illustrate the potential difference in scores.
The GS showing on your character takes into account your 3 weapons and your 6 year pieces. For example, if you have all 229 weapons and 268 gear pieces, your GS would be 256 on your screen: (3x229 + 6x268)/9 = (687 + 1608)/9 = 2295/9 = 255.
The GS for DZ purposes looks at your highest GS non-sidearm weapon (primary or secondary) and your 6 gear pieces. Using the same example above, your DZ GS would be 262: (229 + 6x268)/7 = (229 + 1608)/7 = 1837/7 = 262.4 or 262.
From the info you gave in the post, here's what your toon has equipped:
Chest - 256
Mask - 204 (256)
Pads - 204
Pack - 204
Gloves - 204
Holster - 256
Primary - 229
Secondary - 229
Sidearm - 204
Note: You said that without the mask you have a 256 chest and holster and the rest, as well as your sidearm, are 207. Since the changes GS that put weapons and armor on the same scale, those 207s would have to be 204s.
Without Firecrest mask:
LZ GS - (2x256+2x229+5x204)/9 =221.1 or 221
DZ GS - (2x256+229+4x204)/7=222.4 or 222
With Firecrest mask:
LZ GS - (3x256+2x229+4x204)/9=226.9 or 227
DZ GS - (3x256+229+3x204)/7=229.9 or 230
So, based on the above info, it looks like your issue is that you weren't aware that LZ & DZ GS are calculated differently, because you should have a LZ (displayed on your character screen) score of 227 and a DZ (hidden) score of 230.
Hopefully this explains what you're seeing. If you don't think this is correct, double check my math or post up an issue on the official Ubi forums for the game.