[zaroth]

I must have been holding it wrong. </s>

Seriously though, they must have a very high gain antenna to get 4km range at 2.4GHz with streaming video at unlicensed power levels, so there probably is a very specific antenna and controller orientation you are supposed to maintain to achieve that range.

[StavrosK]

I got it to go 2.5 km away on a very long beach, so it always had line-of-sight. It didn't lose control, so I imagine it could have gone farther (but probably wouldn't have enough battery to come back).