Treatment of the Perez horizon brightening component

[Michele]

Good evening,

I have a question about the treatment of the 3rd component "horizon brightening" of the Perez model for what concerns the shading, as reported in the release notes on the website.

Is it treated like the beam/circumsolar components (purely geometric-analytic shading factor varying with sun position and calculated dynamically) or like the isotropic diffuse/albedo component (constant shading factor depending only on the system's geometry)?

Or even, as it's coming from the horizon, in the case of multiple shed rows, is it null except for the first one?

Hoping someone may answer my question,

Thank you

Best regards,

Michele