The main thing is birds on the field feeding, and seeing more coming in. If you see a group of birds on the stubble but no more coming in from anywhere, then put them off and see what happens. They may just go somewhere else because theyre not that bothered. The best picture to see is one that is building. Then you can watch flght lines to determine where to put the hide,but its the interest the birds have in that field that will determine wether to shoot it or not. Years ago I would watch a field for a week or so but nowadays I would shoot it pretty quick because I think things have changed.
Pigeon shooting is wild hunting and as such there will be disappointments and you have to take them.
I havnt had the air pro that go round just the thin papery ones that flap. I didnt bother changing to real birds because they worked ok on there own. Good luck anyway,youve picked the best time of year to start.