Try adjusting the P25 settings. This means going into the menus a few layers deep. Select your system, then select sites. I'm assuming the Macon/Bibb system is simulcast, so select that site. You will see menu items called P25 Threshold and P25 Adjustment. Change from "auto" to "manual" and set the level to 7. I have found that setting works on many P25 simulcast systems, but your mileage may vary and you might find a lower or higher value works for your particular system. Also, try changing the location of your 536, or adjust the antenna - for 700,800mhz systems keeping the antenna short is typically better. Using a gain antenna can actually make things worse in some cases.
What kind of signal strength do you see for this system?
BG..