Lack of aircraft in 'Defiance'

I think it was the episode before the last one, where someone explained that there is no airplanes because there’s too much radiation (or something) above 400 feet. Does this make sense to anyone? What if the surface elevation is above 400 feet? What if you walk up a hill? Is this magic radiation that maintains 400 feet AGL? If so, why not just fly at 200 feet? (Unsafe in a jet, but perfectly doable in a piston-engine airplane; or a helicopter.)

Fanwank: Side-effect of the terraforming process. Whoever did it would be arriving in space suits and starships and wouldn’t care much about high wind, radiation or the occasional meteor strike. And, it keep those uppity settlers in their place. Also, there’s the possibility of the Avatar reason: “We’re not the biggest thing up there.”

Bad science: Damnation-alley style bad zone 400 feet up, kind of like an inversion layer. How that last 400 feet of air stops radiation and “razor rain” is beyond me.

Bad writing: They’re saving flying vehicles for a future game release and haven’t figured out how to do high-speed, high-altitude aerial combat, so they’re keeping it more to ground level like the speeder bikes & such they used in Star Wars (the things on Hoth that took down the AT-AT walkers).

Or some combination of the above.

Seems like they could at least use hovercraft. But maybe all the hovercraft are full of eels.

Terraformed eels.