There could be higher interference in that direction from the signal lines -- kinda surprised Spektrum just has a single dipole for this brick. Almost every RX they sell these days has a dual whip for diversity and I'd think they'd take the time to do that . . . or at least leave in a SAT plug.
Spektrum gear should be better than 1/2mi, but they were likely designing it for close in. Another knock against this design, I'm afraid, but a gentle one, since 1/2 mi (2600') is farther than most will fly something 350mm in width. A full range Spektrum RX with a full range TX properly setup with satilites to prevent shadowing and polarization loss have been tested to function out to 3mi. I wouldn't expect this to be typical, but half that should be easy. I have no idea how good the built-in reciever is, but the singe whip without an extended, sheilded second antenna implies it's a cut corner.
One thing to note -- where was your TX antenna pointing? I'm assuming it the RX antenna, in the frame is pointing straight down -- if your TX antenna isn't alligned with that, you're loosing signal power.
The vertically polarized RX antenna (pointing to the ground or the sky) paired with a horizontally polarized TX antenna (pointing to the side) will loose 3dB in power -- That's HALF of your signal lost to the antenna not pointing the right direction. unfortunatley, due to spreading losses (circles gain area proprtional to the square of the radius, not proprtional to the radius), it won't equate to doubling your range . . . more like +70% of your range. If that's the case, though, it would put you past the 3/4 mi mark . . .
. . . and make your quad smaller than a speck -- I've visually lost a quad bigger than that at less range . . .
. . . and never saw it again.
