How to determine the formula to calculate this position of reflected Sun?
When the &quot;sun angle&quot; is zero, the position of the &quot;sun&quot; doesn't depend on the season angle, so the lines will cross at the point that is the image of the sun at &quot;sun-angle 0&quot;
One important aspect in your model is that the season doens't change the &quot;angle&quot; but the position of the sun.  In summer, the sun rises and sets in the north East and north west and describes a small cirle around the north celestial pole. In winter it rises and sets in the southeast/west. And only at the equinox does it describe a great circle.