[Al Skierkiewicz]

Nick,
In addition to some of the good info here, the best reception using the antennas supplied is to have them parallel. The minimum coupling between antennas takes place when they are at right angles to each other. The radios do in fact, have two antennas, one external and one internal. At the RC modem, the external antenna is receiving data from the OI, and the internal antenna is sending data back to the OI. Although the dashboard data is affected by this antenna, the software will allow communications with errors on this return link. (according to IFI reps)
As always, mounting any antenna near metal, causes it to detune. This effect is at it's worst when the end of the antenna is near or touching other metal parts. By their nature, antennas of this type, mounted on robots that travel near the ground, would have the best coupling when in a vertical orientation. That is why the IFI supplied antenna farm at competitions is in the vertical orientation.
To use another type of antenna would require retuning the output coupling of the radio, something most teams are not equiped to handle. The band that our radios use have specific limits set by the FCC that allow unlicensed operation in that band. One of those limits is Effective Radiated Power, ERP, which is affected by antenna gain and output power. The majority of teams would not be able to measure ERP so it is ill advised to try to increase that specification.
You can however, move the radio closer to the field and feed it with a longer serial cable. Be careful that the cable you use has low loss as the power for the radio also runs in that cable.