@Alex.A the 2/5 is the Excel fraction format. I add a line with the 1/sensor size and I put your number. The sensor size dont change the conclusion because I only use the pixel size and the aperture to calculate an optical light factor.
The pixel size of the front camera (FP3 and FP3+) is an estimation. Do you have mode data ?
(I speak my approximate english to another comrade)