I have been Recently thinking similar. I'v been using 0% matching from 2D - 3D which im thinking of changing.

In my opinion setting your cm 360 in ratio with Pi (3.142) isnt such a bad idea.. That is the maximum distance your cursor can travel across your monitor equals one full 360 ingame. Your dealing with the two extremes in terms of relative mouse movement.

cm 360 / Pi

In my situation using a 4:3 FOV of 90 (106 16:9) yields very close results to the 100% monitor matching option.

40cm 360 / Pi = 12.73 (100% monitor match is 11.82cm)

Food for thought

So basically because of :math: this is only true because what you're basically doing is finding the 100% match distance for an fov of 114.59. Which is relatively close to 106.26 so by extent the 100% match distances will be similar. In other words dividing it by pi is completely arbitrary.

Math follows:

100% match distance for monitors can be calculated by:

fov/360 * (cm per 360) = match distance

for example 106.26 would be

106.26/360 * 40 = 11.81

When dividing 40 by pi to get your match distance you're multiplying 40 by a fov/360 such that fov/360 is equal to 1/pi. So you solve the equation:

fov/360 = 1/pi

and find that fov = 360/pi = 114.59

In fact since this is all linear you can just find that 12.73/11.81 = 1.078

and then 1.078*106.26 = 114.54 which is only off due to my rounding to two decimals.

Also want to point out that that fov of 114.59 is also completely arbitrary because when dealing with degrees pi has no significant meaning. Pi is only significant to measuring angles when using radians.