Does anyone know a formula, way, ... to make a FPS player feel like an object has the same size on different FOVs (given that it's at the same distance of the player, of course)? I know that this can't be done perfectly, because of the distortion various FOVs cause and the position of the object (near the edges of the FOV = more distortion). Let's ignore these distortions, and aim for a same size feel for objects that are directly in front of the player (so in the exact center of the FOV).
To clarify things a bit further: I want 1 object in my game to have the same scale feel on different FOVs, not my entire game world.
I've tried giving it a percentage of the frustrum height, but that doesn't seem to give me consistent results.
Note: I'm using vertical field of view in my game.