The issue with games like RE2 is that the variation is huge. You might get twice or half the calculated 360 distance based on your DPI and how you move your mouse. Some games like all the Serious Sam games have issues too, but it's more consistent. If it's always off by say +/- 10% I can make a calculation. What I possibly can do is to see if RE2 etc is consistent at any kind of (human) movement and use that as a reference with the game notes informing that e.g. small movement will be off.
Regarding the automatic FOV conversion, I'm going to implement that very soon. Updating all games will take months (there's over 500 games and almost 2000 entries to go through), but I'll make an update that informs you that FOV has been calculated and you need to verify that it's valid for the games that haven't been updated.