TDD PTP with odd throughput values

I am using two Force 180's for a short distance Point to Point link. They are both running Firmware (because of DFS requirements) and are using a 40 Mhz channel.

We are using TDD PTP - only because I need (want) the PtP SM to be able to default over to a sector should the PtP AP fail (the PtP AP and PtMP sector are both on the same tower though very different channels).

They connect with RSSIs in the mid 40's and MCS of 15 on both upload and download legs. When I speed test the link with no subscriber traffic on it, I get ~150 Mbps download and ~50 Mbps upload. This is consistent.  I expect 150 Mbps on a 40 Mhz channel that is 1/4 mile apart.  What I don't expect is the 50 Mbps upload.

We are running in flexible mode, 5ms frame.  It is acting like it is in a 75/25 GPS mode, not flexible. 

how many uplink retransmittions or errors are you getting?  

a busy site with noise will slow the radios down. also if there is traffic on the link, and its already tilted bandwidth wise one way or the other, that can be carried over to the link test results.   the link test won't stop your active traffic to give you a high score. 

Link testing was being done with no client traffic on the link - just my link test traffic.

From my last re-boot yesterday:

1 "error drop packet" on the uplink

7402 "re-transmission packets" (1.5%)

Not noisy and not a very busy site. This is a small backhaul link feeding a 1000 GPS AP with 5 clients on it currently. There are 2 1000 GPS APs in the immediate area but one is 5.1 and the other is 5.7.  This link is at 5550. RF scan is dead quiet in DFS channels.

almost 100% of the packets at MCS 15 both ways?

This is from the client end after 3 hours of stat collection (done a fair amount of re-booting to trouble shoot and test options):

I can back the uplink from the client down to 13 or so but I don't think this is the issue.

thats really odd.   wouldn't hurt to test locking the modulation down and see what happens, but I'd expect that link to show a much better uplink result than 50 

I have tried a few frequencies. All very clean. Same exact results.

If I move the AP into a 50/50 mode from flexible, I get 113/115 Mbps every time I test.  When I switch back to flexible, I get 145/58 every single test. Again, this is with no client traffic at all on the link.

So, I am beginning to conclude that (and others?) has an uplink/downlink ratio problem in the flexible mode, at least with a 40 Mhz channel in DFS.  Cambium, can you test in your lab?  This is between two Force 180 radios.  Clearly the radio is able to do faster speeds since it works in 50/50 mode (where I am going to leave it for now).