5 GHz Wi-Fi 6 super weak signal in vertical direction

Hello, I have TO with WiFi6 upgrade kit installed in a lower storey of a two-storey house. I would like to use a laptop on the first floor, approximately 2 meters above and 1 meter away of TO. The problem is that the 5 GHz signal in this position is so weak (-80 dBm and worse) that it doesn’t work. 2,4 GHz works absolutely flawless.

I know radiation diagrams of the antennas and that above them is uncovered space. But several things puzzle me:

  1. Changes of antennas’ alignment make no difference. Both bending them upwards (90°) and leaving them positioned vertically provide the same bad results. Why?

  2. The antennas are the same, so why 2,4 GHz works perfectly?

  3. Before installation of the Wi-Fi 6 kit, the 5 GHz worked fine. I’m nearly sure that I installed it correctly. Moreover, if I go few steps downstairs, perhaps 1 meter down, wifi6 starts working in full strength as expected.

Any suggestions what could I do to get it working on upper floor?

Did the previous 5 GHz wifi work fine in the upper floor? You might have some steel rigging in the floor that hinders the signal.

Also, recheck the antennas (mostly the inner connections).

Also, do you use diplexers? Can you try without them?

Yes, I use diplexers. My setup is the same as the one described in wifi6 upgrade kit installation manual.

Some steel parts in the floor are possible, but I don’t expect anything that would cover whole upper floor. Moving laptop on the upper floor make no significant difference.

Yes, with the previous wifi 5 GHz card it was working fine.

It seems that you have connected antenna cables to wrong diplexer input - can you check if it is connected right (2,4/5GHz)? Especially if the older 5GHz card worked fine.
Newer diplexers have switched sides according to the older diplexers. Text on them is small, so it is no problem to connect it wrong.

Or, maybe, have you tried to reset wifi settings in reForis and set wifi from scratch?