For the best performance and easiest setup, when using multiple channels of IEM they should be connected to a combiner and then retransmitted via a single helical antenna using the lowest gain setting that reliably works on your transmitters. The use of  multiple transmitting antennas on multiple transmitters almost always results in signal degradation. We recommend feeding no more than eight transmitters into a single combiner system as exceeding that number rapidly increases the probability of IM (intermodulation) interference and results in the likely reduction of possible open channels for both your mics and ears.
Helical antennas are overwhelmingly the antenna of choice for IEM transmission because the circular motion of the RF field emitted distributes the signal through all possible polarization angles. This removes the greatest risk of dropouts, as most IEM belt packs are limited to a single whip antenna.
Using Mics and Ears Together Strategy
IEM Combiner