I'm pretty sure whatever conversion is going on for between "Hdeg 4:3 fov" and the APEX legends FOV multiplier is wrong.
I believe this is the correct formula for Hdeg 4:3 to multiplier conversion:
1 + ((x - 70)*(0.01375))
where X is the Hdeg 4:3 fov value you want
Why do I think this is correct? My aim always felt off using the current settings the calculator gives so I knew something was wrong. First, I confirmed that the mouse sensitivity calculations were correct by using an autoit script to do 360, and the calculations are correct so I knew it had to be FOV issue. Next, I realized that the in-game FOV slider is moving the multiplier by a constant value (0.01375 per 1 FOV). Which means if you manually set the FOV config multiplier value in the profile.cfg file, it will be moving at that constant when you move the slider. After that, I realized that 70 fov in game will always set the cl_fov value to 1. I concluded this a "0 point" I can use and that moving at increments of 0.01375 per 1 FOV will yield the proper HDeg 4:3 FOV because it is based off the source engine. Sure enough, when I did the calculations and set FOV to the proper FOV that I normally play on other FPS games (86.6 HDeg 4:3 FOV), my aim felt normal again.
Here's a JScalc I made for people who are lazy to do math: https://jscalc.io/calc/sjaxm3vHaXvjqmf5