I've been using two LHG LTE6 kit devices. One of them is in a remote rural location, over 4km to the cell tower, with dense forest. I don't expect miracles there, but it works just fine.

But the other one is in a city, where the cell tower is 520m away, no buildings in the way, just low bushes and several trees (a park). In winter, when there is no foliage, I can see the cell tower. And I'm puzzled by the signal quality numbers, they seem low, and I never get great performance. My downloads are 6-20Mbps, the uploads are better at around 20-30Mbps. The download speeds are comparable to my remote forest location!
Are those the numbers one should expect from an antenna aimed at an almost-visible cell tower 520m away?

I verified that the enb-id corresponds to the cell tower I'm aiming at. It's the only one visible in that direction.

Am I doing something wrong?

Do you have a Modern 4+y old smartphone best with 5g support that will have QAM 256 and cat 18 LTE modem where you can install this simcard and test Full capabilities of tower speed?
and Put Cellmapper screenshot next to it

But based your current UL are better Then DL speed I suggest that tower is just too congested and Uplink to tower isn't good enough.

Signal Quataly and SINR isn't the best I think there is interference from other towers, Try to move around and find some shield

@jrychter; are you totally sure you're aiming the antenna at the right tower? There's an easy way to check this. First, run a speed test on your phone to enable CA (carrier aggregation). Then immediately put your phone in field test mode and compare its cell IDs with the ones in your LHG.

I am sure I am aiming at the right tower, I verified the enb-id with a cell tower map.

Unfortunately, comparing things with a phone won't help, as phones have become so dumbed down. My iphone won't tell me anything.

But my questions were more about how reasonable those signal quality numbers are: I have a feeling I should be getting better than -91dBm RSRP if I'm aiming the antenna at the tower. I did some experiments moving the antenna (in case I'm not aiming it precisely at the tower), and the best RSRQ I've seen was -15.5dB. That's only 520m of distance!

...

At that distance, you should get at least -10 dB (RSRQ). It's the signal strength that makes me wonder it might be the wrong tower. Put your iPhone in field test mode by dialing: *3001#12345#*. Check the connection IDs and compare them to your LHG.

EDIT:
We've got a whole bunch of customer setups with LHG/LTE6, and I just checked one that's about 1.4 km from the tower with a forest in between, and even there we're getting -8.5 dB. Average link speed is approx 90/30 and with an average round-trip time (rtt-avg) of 28 ms using "CA always on".

Thanks, @Larsa — that would indicate the numbers do indeed seem off. I'll verify the cell id with the phone.

Ok, so I tried to verify with my iPhone. I can't get the phone to connect to the same cell tower in the location where the antenna is. There is another tower in the opposite direction (which I can't use for the LHG LTE6 kit antenna) and the phone really wants to switch to that one.

But what I did was get much closer to the cell tower I'm aiming at, to see how things would work there. And the phone speedtest was much better than what LHG LTE6 can do: 71Mbps/34Mbps. But the signal strength wasn't that impressive, either: RSRP -98dBm and RSRQ -20dB. That was less than 100m from the tower and I could see the antennas.

Could it be that I'm just unlucky and with the way the antennas are placed, my LHG LTE6 is in a direction where the signal is weak?

I took a picture standing fairly close to the tower, but in the same direction as my LHG LTE6 is. I also marked the direction on an aerial picture. It does seem that my direction is not where any antenna points, and this would make business sense (there is almost nothing in that direction, and there is another tower serving that area, 800m further).
So, would that explain the poor performance of the LHG LTE6?