stereo3D

have you fiddled with the in-game sliders? looks like they are additional multipliers for x- and y-axis.
not sure if it's worth adding support for them, but the notes should probably tell the user to leave them at default.
one big problem is that mouse movement at lower sensitivities gets ignored.
with MouseSensitivity=4.427166 and 1000 DPI it won't let me aim upwards unless i move the mouse pretty quickly.

using the sensitivity slider causes the ADS sens ratio to go completely out of whack.
it's best to leave it at default and change it in the config. config sens seems to be like ut3.
%USERPROFILE%\Documents\My Games\Bulletstorm Full Clip Edition\StormGame\Config\StormInput.ini
MouseSensitivity=6.0
bEnableMouseSmoothing=false
%USERPROFILE%\Documents\My Games\Bulletstorm Full Clip Edition\StormGame\Config\StormCamera.ini
DefaultCameraFOV=120
TargetingFOV=60

hor zoomfov / hor fov (named 100 % monitor distance in the calculator) has always felt best to me. i preferred it on 4:3 crt and still prefer it on a 16:9 monitor.
when i zoom in while moving the mouse horizontally, it feels like the sensitivity stays the same.
anything less than 100 % feels like a slow down. 0 % is unplayable for me.

yes.

the config is overwritten by steam cloud (options - steam cloud - disable).
there are options for raw input and FOV  (options - multiplayer - FOV).
fov_desired "104.821821"
cl_viewmodelfovsurvivor "90"
m_rawinput "1"

i don't have the game, but in case there is no mouse smoothing option:
input.ini
[/Script/Engine.InputSettings] bEnableMouseSmoothing=false

Checked it now and you're right, it's 66.67% (i.e. 2/3) of the horizontal.

Sensitivity in this game is such a complete mess, but I've manage to add ADS now, and fixed the FOV calculations. For some reason the FOV at 70 is 80 in third person mode and 70 in ADS.

Try again now, was an issue with the lack of console options for the Microsoft Store version.

Nice, added now. Note that the game only reads the first two decimals, and going below 1 causes a lot of reports from the mouse being lost so I've set the minimum to 1.

Done

ok, that means ironsights/1x optics have a 0.9 fov multiplier and a 0.6 sens multiplier.
 
imho it's best for muscle memory when fov multiplier and sens multiplier are identical.
in order to achieve this the calculation is:
 
0.9/0.6/0.02=75
 
AimDownSightsMouse=75
XFactorAiming=0.020000
 
the only difference to csgo is that r6 siege uses vertical fov, whereas csgo scales with horizontal fov based on 4:3, but the difference is miniscule.

Added now!
That naming sure made it easy lol!
Just a multiplier (2.6) to the sensitivity but a true 2X zoom on the FOV, so it doesn't really align with any scaling.

Added!
No One Lives Forever 2 is also in, the mod worked

Updated!

i think it would be better if the result got displayed more like this:
Mouse Sensitivity 2.00
1x Optic / Iron Sights 1.15 (1x Optics, Ironsights (SMG, SG, Pistol))
1x Optic / Iron Sights 1.22 (Ironsights (AR, LMG, Sniper))
2x Optic 1.42
3x Optic 1.54
4x Optic 1.59
6x Optic 1.62
8x Optic 1.63
10x Optic 1.64
 

I guess the called it "FOV Scale" for a reason..
Just checked the game and found out how it works, so the game is updated now. Calculations are now also 100% correct, they were off by a few counts before (because of how the FOV actually works).

it should be possible to adjust the sensitivity more precisely in the config.
original: %APPDATA%\Bioshock2Steam\Bioshock2SP.ini -> MouseSensitivity=1.234560
remaster: %APPDATA%\BioshockHD\Bioshock2\shared.ini -> MouseSensitivity=0.123456
 

the patched in fov slider in the remaster seems to be based on 16:9 aspect ratio.

some older entries have the wrong fov type. until this is fixed you could select deus ex goty and then set the FOV to 120 (or 121.664773) to calculate your sens.

I've actually already updated this in the upcoming version that supports separate vertical sensitivity. Hope to publish it in a few days.

Done!

Added 👍

This was quite a bit of work to get done! The different FOV mods work differently, and how the base game calculates FOV is pretty weird. But added it all now

Done!