I can only speak for Reaper/Predator as they have forward looking cameras and also the sensor ball can be slewed forward - you can read the registration on a C-17 from 15+ miles.
But how was the C-17 spotted in the first place, to allow the operator to zoom in on it?
I'm genuinely curious as I have extensively flown DA42M with backseat operator and with the same FLIR as Reaper. I also have some experience as operator in the back. I would say that just about every time we have spotted a target, whether on the ground, in the air or at sea it is initially spotted by Mk1 eyeball of one of the onboard crew. The field of view and acuity of eyeballs is still way ahead of the sensors and video screens that I have flown with.
Of course, once the target is zapped and locked with the laser, and the sensors zoomed in, the detail visible is way better than eyeball. But finding the target in the first instance is almost always requires an eyeball in the loop.