Radiometric conversion of sentinel 2 images

[Igor]

It seems to me that this formula is correct:
L = (UrToaESUN*cos(theta))/PI;
Watch the discussion here:

Distance of Earth-Sun

Hello all! Who can explain under what formula the calculated value of the distance Earth-Sun in the metadata file S2A MSI L1C product? Why ask this question? For example, for the S2A data from 3.01.2016 this value is: 1.03423414807786 However, in such sources as: Mather, Paul M. Computer processing of remotely-sensed images: an introduction / Paul M. Mather and Magaly Koch. – 4th ed. Page 120; Applications of satellite and airborne image data to coastal management. Seventh computer-based…