Oof, answered my own question I think.
Northrop's ground-portable laser designator system is a bulky handheld size, can rangefind out to 60km and designate Paveway targets to 10km. That's about thirty-three thousand feet, and that's at gound level where atmospheric dissipation of the laser beam is at its worst.
You have to assume a high-class drone is going to have as good or significantly better system than that. So in English, it means a Reaper drone can very likely precision-drop its weapons from anywhere up to its maximum flight ceiling, which is published at 50,000 feet.
Even if the rocket motor of the Hellfire II would be long expended before that, the fall is more of a controlled glide, with gravity being the fuel and the guidance system working just fine all the way down. Same with any of the Paveway-equipped bombs.
You ain't engaging that with anything smaller than a flying telephone pole with a damned good RADAR. Scaaaaary!