For anyone interested I have confirmed that the in-game value is without a doubt wrong. The correct 4:3 FOV is multiplier*70. First for reference I did the following in CSGO where we know the FOV values are exact. Took a screenshot of an object at FOV 70, 80, 90, 100 and 110.
FOV VDEG Pixels Pixel ratio FOV ratio Error
70 55.41 556 1.000000 1.000000 0.00 %
80 64.37 464 0.834532 0.834366 0.02 %
90 73.74 390 0.701439 0.700161 0.18 %
100 83.58 328 0.589928 0.587525 0.41 %
110 93.93 273 0.491007 0.490285 0.15 %
As you can see the ratio between the FOV and pixels is pretty much spot on.
Doing the same for Apex assuming the in-game value is correct gives the following output:
FOV Multi VDEG Pixels Pixel diff FOV diff Error
70 1.0000 55.41 555 1.000000 1.000000 0.00 %
80 1.1375 64.37 464 0.836036 0.834366 0.20 %
90 1.2750 73.74 396 0.713514 0.700161 1.87 %
100 1.4125 83.58 333 0.600000 0.587525 2.08 %
110 1.5500 93.93 278 0.500901 0.490285 2.12 %
The error is clearly increasing with the increase of FOV.
If we instead assume the FOV is multiplier*70 we get the following:
FOV Multi VDEG Pixels Pixel diff FOV diff Error
70 1.0000 55.41 555 1.000000 1.000000 0.00 %
80 1.1375 64.05 464 0.836036 0.839557 -0.42 %
90 1.2750 73.02 396 0.713514 0.709404 0.58 %
100 1.4125 82.45 333 0.600000 0.599315 0.11 %
110 1.5500 92.35 278 0.500901 0.504015 -0.62 %
All this is just confirming that the FOV measured in-game correlates to multiplier*70 and not the in-game value.
Images attached for reference.