Solar Sensor Set-up

Can someone tell me the correct way to setup the above when the box is ticked for “Update the Maximum Solar Value from this maximum reading for lat/long, daily”.

The system works fine (so far) with the parameters I put in when the box is unchecked, but if I tick the box, the parameters change, so when it is sunny (100%) the "Maximum radiation for daily) indicates something like 729. I see that the box that shows Degrees C = 100% reflects this same number of 729. With this, I have “Overcast/gloomy” presented and the current % reading indicates 1.2% instead of 100%.

Any ideas please where I have gone wrong.