In the foreground of Rory's composite picture in post#36 we have a lamp:Well we're not seeing the drone, we're seeing a light (including glare).
If the lamp is (say) 17 m from the camera and the drone is (say) 215 m then if the lamp was on the drone the glare measured by the camera should have a width w given by
w = 17 px * (17 m / 215 m) = 1.3 px
On a picture of the object this looks like
Therefore if the object is a drone at (say) 215 m then it is being illuminated by something much more powerful than the lamp in the foreground.