Any idea how the wifi signal wave spreads from extender?
It depends on antenna being used, but most probably you have ominidirectional one, so extender range looks (roughly) like a lens, with antenna in the center, plane perpendicular to antenna. So, it's easier to get out of reach by flying up.
Directional antenna should give you better range, but you'd have to keep it pointed in flight direction, as it's range is... well, directional There's a short article with diagrams that show differences better than I can explain here.
Of course, there are many sub-types of antennas -- you should be able to find these diagrams for your model, if needed; but in everyday usage more important is to have clear line of sight between antenna and drone. So, it's good to put extender on some kind of elevation (say, photo tripod ) to avoid ground obstacles.
Nice set up WiFi. No offense, but I prefer something smaller and transportable! although yours is certainly resealable and compact.Ha, cool! I use an almost identical setup, except I use a studio light stand (higher than reg. photo tripod, for lighter items, very cheap usually). I use a usb extension cable to power the little Wifi paddle from the charge 'brick' below which I also use to charge batteries in the field. (currently Xiaomi Mi '1', version '2' is on its way...). Maybe the wind lets off later and I can go out and do some flyin' and take a pic of it all. Here, I found these little guys for a mere $14 (before shipping.)