@pk123 but even if the sun's elevation was never at 90 degrees to the sunshine sensor over a 5hr period the angle would've changed which would change the amount of irradiance measured by the sunshine sensor.
For example assume there was a 10 degree elevation change for the sun from 40 to 50 degrees over the 5hr period, that's the difference between cos(40) = 0.77 versus cos(50) = 0.64. So I would expect to see a difference in the CH0 counts over the interval.
Now the Sequoia sensor has a GPS and IMUs (one for the sunshine sensor and one for the RGB&Multispectral sensor) so in theory they could work out the sun's angle relative to the attitude of the sunshine sensor in realtime but I'm pretty sure they don't. Instead they simply record the attitude info in the IrradianceList tag so that you can use it in post processing.
For example in Pix4d you'll notice the following info comments during post processing:
Info: cos(sun, irradiance sensor) 0.573237 direct sunlight fraction 0.933341 correction 0.853415