Horrible signal to noise ratio

First I would only run one fan and make sure its blowing bottom to top and you have spacers under the fan so it can draw air in from under it. Fans can cause interference noise sometimes, one at the bottom blowing up is more then enough to help push the passive heat dissipation faster. You can out a piece of single layer tissue on top to see if the fan is pushing enough.  I noticed sometimes if you turn the fan a certain way it can push more.  If this is a 12V fan you wont need to run it at 12V as that could just cause more noise interference so I suggest running it at 5V from a USB power supply. 

Have you done a full default reset on the unit since you found a good spot with the good secondary signal? I have also seen others mention that it needs to be unplugged for 3 minutes before plugging back in. Maybe the secondary signal is active but not fully online yet?  You could call T-Mobile and ask, or maybe they dont know the tower is having any issue unless you report it.

Mine is running the same channels of B2 primary and n71 secondary (see attached picture).  I have attached my speed test results also. I found that because of the way speedtest does the test sometimes the servers cut back on the upload speeds, so I started running it from my router that's that I use off the ethernet. My router is 22 feet away on the other side of the room. I did this to also avoid unwanted interference as listed with the FCC Part 15.
This device complies with part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation.