You used this -exact- same antenna setup with a Mikrotik and a Ubiquity product and the ePMP works worse? If everything is the same except radios, how much worse?
Have you tried removing the gain antenna and testing with the 2 standard antennas that screw directly to the radio?...comparing range.
Also, what model coax are you using (RG-58, RG-59, LMR-240, etc)? What condition are coax and connectors? Has coax connector/s been properly waterproofed?
If you are using 2.5m of RG-58 you will have about 2db (40%) of signal loss (with coax and connectors in good condition). In reality this is not that huge of a drop since you are using a 12db antenna (if that is the true gain of antenna and not marketing hype).
You would have better results using two identical antennas with short sections of coax.
