My asking the questions was aimed at trying to show that for most any practical panel size here on earth as compared to the distance to the sun generally will give almost equal irradiance to the four sensors through quote a range of panel angles. Your comment about mounting the sensor inside a tube solves this problem rather nicely.

Clearly there are also some issues with tube diameter versus length as well. A tube say 10 mm in diameter but one meter in length would be VERY directional but it would take a LOT of search time to find the sun, particularly on dual axis adjustment system. It would be simpler for a single axis system.

The tubes offer the same type of solution as the shading fins on the one type of tracker that was shown in one of the linked pages given on one of the other posts. In that solution there were two tanks, each containing a fluid and interconnected by a small tube. The shading fins offered a directional access to sun irradiation on the tanks.

Michael Karas