I recently switched my piaware setup, (Pi 2 + Orange FlightAware Pro) from using ethernet to wifi. Its in exactly the same place. The only other difference being FlightAware is now on a short 1ft USB extender cable ( it was covering all the USB ports) so that i can plug in a usb wifi.
I’ve noticed my # of aircraft drop down to about 25% of my usual total.
Can the wifi be interfering with the reception? I can provide pictures of the setup if needed.
Setup is indoors, sitting on the window sill.