When testing my SXT LTE6 Kit I noticed that the CA Band only appears when testing download speed, but doesn't appear when testing upload speed. Is this the expected behavior and it works for downlink only, or does it depend on ISP, or do other special criteria have to be met for carrier aggregation to work on uplink?

Also, the cell tower my SXT LTE6 Kit connects to is about 70m away, across the street, with a clear line of sight and Fresnel zone (I can't connect to any other of my ISP's towers as I'm surrounded by tall buildings and this is the only one I have clear LOS to, also it's the closest one), and I'm getting very strong signal (RSSI -47, RSRP -56) but mediocre SINR - about 9 dB but it varies from 4 to 15 sometimes.
For comparison, another SXT LTE6 Kit I have configured is in a rural area and has about 650m to the cell tower, but gets about 25 dB SINR.
Could this low SINR at my home be caused by city interference, large amount of nearby LTE users, multipath interference, or something that I could have done wrong? The cell tower I'm connecting to serves one other ISP besides my one (same situation at the rural area SXT), and there's also much closer tower belonging to a different ISP on a neighboring building about 10m away, it's at a direction that is perpendicular to where my SXT is pointed, the antenna shouldn't have much gain in that direction, right? Unfortunately I don't have any windows where my SXT would be fully shielded from it.
I have also suspected that the modem could be getting overloaded because of the close proximity and considered installing attenuators between the modem and the antenna array, but haven’t found any with u.FL connectors.

Also, when I opened the case, I noticed that besides the LTE antenna array in the middle, there are also two F-shaped prongs on the sides. They are also visible on pictures in this thread. What are they for? Are they part of the LTE array or something else? (Edit: Are they for LTE800 while the center array is for higher frequency bands?) At first glance they look like thay would receive signal from the sides of the SXT instead of from the front, but I'm not sure if I'm looking at them right. I also found a radiation pattern that someone has generated for the array, but the prongs weren’t included in there.

The speed I'm getting through the LTE connection is about 30 Mbit/s down and 20 Mbit/s up, and mostly the B7 band is used. It works quite well, but I'm wondering if anything more is possible along with better stability (which is the reason I'm using an outdoor modem). I'm using it as a secondary connection for remote access, my primary one is a much faster fiber connection.