Found some interesting reading....
http://community.cambiumnetworks.com/t5/ePMP-Troubleshooting/What-is-front-to-back-ratio/m-p/47818#U47818
http://community.cambiumnetworks.com/t5/ePMP-Synchronization/Mitigating-self-interference-in-an-ePMP-ABAB-frequency-reuse/td-p/38203