RBR750 / RBS750 Backhaul 'Poor' & slow speeds

I've downgraded the firmware on my RBR750 / RBS750 system to 3.2.18.1 due to unstable v4. The system seems much more stable however the speeds are not great: I have Bell Fibe 500Mbps up/down service, and on devices connected via 5Ghz band I'm getting 100-120Mbps at most.

In the 'Attached Devices' page (web ui admin) both satellites's Backhaul status shows as 'Poor'. The satelites are about 50ft away from RBR.

The settings in RBR750 are:

• CTS (both 2.4 & 5Ghz): 2347
• Transmit power control (both 2.4 & 5Ghz): 100%
• Preamble mode 5Ghz: short
• Preamble mode 2.4Ghz: auto
• AX enabled on 5Ghz only

 I've set dedicated IPs for both satellites. The only other things I haven't tried yet: settig up the satelittes in the same room with the RBR then move them in their locations.

Any recommendations on how to:

• improve backhaul from Poor to Good?
• improve the speed I'm getting on the network overall?