RE: Spektrum radio
I believe that antenna orientation becomes an issue at 2.4 GHz because of the greater path loss at 2.4 GHz, not because the 2.4 GHz antennas are more directional than 72 MHz antennas. Both antennas are designed to be omni-directional to the extent possible.
We don't see antenna orientation problems much at 72 MHz because the signal strengths at the receiver are very high, so only a very severe pattern or cross-polarization null will affect the receiver. The signal strengths at 2.4 GHz are comparatively weak, so a modest null or polarization misalignment will kill the link.
This suggests the possiblity of improving 2.4 GHz SS performance by use of an antenna diversity system... two or more antennas oriented perpendicular to one another in the airplane so that when the signal falls into the null of one antenna it will be received well by one of the other antennas. Since at 2.4 GHz a dipole antenna is only about 3 inches long, having multiple antennas in a 40 size airplane (for example) would be perfectly reasonable. The 2.4 GHz receivers would need to be specifically designed to make use of the multiple antennas with a voting circuit and separate connections for each (connecting the antennas in parallel would not work).