Helmets and face shields will protect the full head.
This simple mod edits helmets and face shields to cover all head hitboxes:
Face, Top of Head, Nape, Ears, Eyes, Jaws, Throat, and Back neck.
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Overview
Enjoy the thrill of being able to peek your head out of cover without worrying about being one-shot in the face by a small caliber. Helmets now work with the rest of your gear as a vital piece of armor. The armor class difference between a SSh-68 (level 3) and a ULACH (level 4) will impact your raids.
This affects ALL helmets, including helmets worn by bots.
**PLEASE READ BEFORE INSTALLING:
All bots have their equipped helmets reduced down to 1 durability by default. This allows players to use small-caliber guns like SMGs and pistols while aiming for the head, as all headshots will almost immediately zero out any bot's helmet.
You can change the above using the configuration file if you want enemy bots to have normal helmet durability. Just keep in mind that this will cause enemy bots to potentially become major threats.
Don't expect pistols or SMGs to be viable for headshotting a PMC if you toggle this option to false. If your bots have face shields on top of a high-armor helmet, you're honestly better off aiming for legs or arms unless you're shooting with M993. Sounds silly, right?
Install
Extract directly into the SPT folder. Mod folder can be located in user/mods/.
Other Mods
I recommend using my other mods, Get Concussed and Clean Face Shields, to receive concussions/tinnitus when your helmet takes headshots and also clean up that visor. 
Configuration
Edit config.json in the mod's config folder:
"ModifyHelmets": true, "ModifyFaceShields": true, "ReduceBotHelmetDurability": true For ModifyHelmets and ModifyFaceShields, set a desired value to false if you do not want helmets/face shields to be affected by this mod.
Set ReduceBotHelmetDurability to false to set bot helmet durabilities back to normal, if you want enemy bots to also benefit from the full head coverage granted by helmets.
Specifics
The armorColliders, Durability, MaxDurability, and armorClass are updated for all helmets. For example, the modified SSh-68 steel helmet (which has default 54 durability) is shown below:
- Plate - Head top - 1/1
- Plate - Nape - 1/1
- Plate - Ears - 1/1
- NEW PROTECTION: Face, Head top, Nape, Ears, Eyes, Jaws, Throat, Back neck - 51/51
In practice, the 51 durability is used for all head hitboxes and receives durability damage when shot at. You can safely ignore if any of the 1/1 plates are lowered to 0/1 since the 51/51 helmet durability acts as the 'top layer' and will be used to block bullets.
Face shields have also been buffed with +2 armor class, to keep them relevant with helmets.
SPT 3.10.5
2.9K Downloads
Updated for SPT 3.10
Unknown SPT Version
227 Downloads
LAST UPDATE FOR 3.9.8
New: Helmet protection will only benefit the player for those looking for an alternative mod to prevent headshot deaths while still maintaining usual game balance. Bots will have their helmet durabilities reduced down to 1 when they spawn into the raid.
Change ReduceBotHelmetDurability to false to disable this feature in config.json.
Unknown SPT Version
480 Downloads
Fixed an error that would occur with headwear loaded in from other mods.
Unknown SPT Version
125 Downloads
Changed how durability works to make it more readable: all helmet plates are now set to 1 max durability, meaning that the helmet's total durability numbers will almost 100% accurately reflect how much full-head durability is left in the helmet.
(i.e. If a helmet has 100 durability and 3 plates, 97 out of the 100 durability will cover the entire head).
In line with moving back to vanilla durability numbers, face shields' durabilities have been moved back to default numbers.
The changes will not apply to current helmets equipped.
Unknown SPT Version
259 Downloads
Added configuration options in ../config/config.json, for setting values if user does not want either helmets or face shields to be affected by this mod.
Not quite yet...