Hi Kevin,
Thanks for pointing out the document. With ePMP, we do not support a ABABAB six sector deployment where only two frequencies are reused. I think the document meant to say ABCABC. I will check into this and get back to you.
My comment was referring to an ABAB (or ABCABC) deployment as explained here: http://community.cambiumnetworks.com/t5/ePMP-Synchronization/Mitigating-self-interference-in-an-ePMP-ABAB-frequency-reuse/m-p/38203#U38203
As for which APs should be set to "Front Sector" and "Back Sector", it is on the APs using the same frequency. In other words, in an ABAB deployment, the AP using frequency "A" should have it set to "Front Sector" and the other AP also using frequency "A" should have it set to "Back Sector". Similarly for the APs using frequency "B". This setting is discussed in detail in the ePMP User Guide available here: https://support.cambiumnetworks.com/files/epmp/. It lists out a few possible scenarios and provides guidance on how this setting should be used.
Thanks,
Sriram