Hi Sheriton,
Thanks for getting back to me. Thanks for letting me know about the lack of relationship between WiFi and Line6 channels, I didn't know! I'll try and switch them to RF1 next Sunday.
In regards to antenna positioning, we currently have the recievers rackmounted - with the antennas coming out the back, inside our case, very close to each other. We have been looking at getting some Coax extension cables and fixing them to the side so that they're a bit more spaced out, and will probably try to get this set up within the next couple of weeks.
Our rackmount case is pretty much on the other side (diagonally) of the hall to where the musicians perform, maybe 10m or so, however I haven't noticed a massive amount of dropouts from over there (although maybe it's because there's instruments and a congregation masking any!). Where I've really been noticing issues is Centre Stage to Stage Left, when people are speaking, probably about 7-8m away from the antennas. I will try to do something with Antenna distribution as, now that you mention it, this probably will not be helping, and I'll read up on the manual a few times tomorrow.
Thanks for your help, I'll let you know how it goes.
-Thom