I’m bummed that no one from A&H has responded – however, I found the answer in the recently posted user guide (pg 44) copied below. I am quite bummed that the LCR doesn’t have “percentage” panning as most other LCR busses do. It doesn’t help me to not be able to have something panned center in LR also (at specified amount, not just LR+M). https://www.allen-heath.com/media/Avantis-Firmware-Reference-Guide-V1.00.pdf
3. Main – Select one of 5 modes of Main mix:
• None – No Main mix, for example dedicated monitor mixing with a large number of Aux mixes.
• LR – Standard stereo Main mix.
• LR+Msum – A stereo Main mix with additional output which is the mono sum of the pre-fade, pre-processed LR mix. For
example to feed a mono delay speaker or zone.
• LR+M – A 3-way main mix with independent stereo LR and mono M busses. Channels can be separately assigned to any
combination of LR and M. Typical application for M is main centre speaker, mono PA or bus-fed sub bass.
• LCR – A 3-way main mix with LCR panning. Each channel can be panned from left, through centre to right. At mid pan, full
signal is fed to M and none to L and R. Stereo channels feed the LR mix only.