There's a few things that I've noticed. Increasing the Min/Max Pixel Threshold to 30, seems to be able to cope with the sun coming out from behind the clouds and vice-versa.
Blobs seem to be more accurate when working with distant movements. The image below is probably 15-metres on the left, and about 90-metres maximum where the white building is.
Percentages aren't really useful when dealing with fine setup.
I had initially set this up at the back of the house, and was waiting so long for Alarms etc. etc. So I moved it to the front of the house where there's lots going on. Tuning the Zones is a bit of a black art I must admit.
Any comments gratefully received.

