I'm repeating the same test I did back in December, same devices and placement.
I'm getting good signal in that test arrangement (VHT-MCS 9, VHT-NSS 2, Short GI for both TX/RX) and signal is not as badly affected by even slightly obstructed line of sight between AP and client as it used to be.
kari@zenbook:~$ iperf3 -R -c 192.168.254.7
Connecting to host 192.168.254.7, port 5201
Reverse mode, remote host 192.168.254.7 is sending
[ 4] local 192.168.254.21 port 42526 connected to 192.168.254.7 port 5201
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-1.00 sec 42.9 MBytes 360 Mbits/sec
[ 4] 1.00-2.00 sec 44.9 MBytes 376 Mbits/sec
[ 4] 2.00-3.00 sec 50.8 MBytes 426 Mbits/sec
[ 4] 3.00-4.00 sec 56.2 MBytes 472 Mbits/sec
[ 4] 4.00-5.00 sec 56.5 MBytes 474 Mbits/sec
[ 4] 5.00-6.00 sec 55.1 MBytes 462 Mbits/sec
[ 4] 6.00-7.00 sec 37.5 MBytes 315 Mbits/sec
[ 4] 7.00-8.00 sec 56.0 MBytes 470 Mbits/sec
[ 4] 8.00-9.00 sec 56.3 MBytes 472 Mbits/sec
[ 4] 9.00-10.00 sec 55.4 MBytes 465 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-10.00 sec 521 MBytes 437 Mbits/sec 111 sender
[ 4] 0.00-10.00 sec 512 MBytes 429 Mbits/sec receiver
kari@zenbook:~$ iperf3 -c 192.168.254.7
Connecting to host 192.168.254.7, port 5201
[ 4] local 192.168.254.21 port 42688 connected to 192.168.254.7 port 5201
[ ID] Interval Transfer Bandwidth Retr Cwnd
[ 4] 0.00-1.00 sec 61.9 MBytes 519 Mbits/sec 0 913 KBytes
[ 4] 1.00-2.00 sec 66.9 MBytes 561 Mbits/sec 0 1.25 MBytes
[ 4] 2.00-3.00 sec 66.4 MBytes 557 Mbits/sec 0 979 KBytes
[ 4] 3.00-4.00 sec 67.7 MBytes 568 Mbits/sec 0 1.19 MBytes
[ 4] 4.00-5.00 sec 65.4 MBytes 548 Mbits/sec 0 1.15 MBytes
[ 4] 5.00-6.00 sec 66.2 MBytes 556 Mbits/sec 0 1.12 MBytes
[ 4] 6.00-7.00 sec 67.0 MBytes 562 Mbits/sec 0 1.24 MBytes
[ 4] 7.00-8.00 sec 67.3 MBytes 564 Mbits/sec 0 1.47 MBytes
[ 4] 8.00-9.00 sec 65.4 MBytes 549 Mbits/sec 0 1.20 MBytes
[ 4] 9.00-10.00 sec 70.0 MBytes 587 Mbits/sec 0 1.19 MBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-10.00 sec 664 MBytes 557 Mbits/sec 0 sender
[ 4] 0.00-10.00 sec 661 MBytes 554 Mbits/sec receiver
I don't see frequent disconnects from the stationary clients according to the logs and of course having ieee80211r configured on the APs and most mobile clients being recent enough to take advantage of that so handovers between different APs and bands seem to be quick enough not to be noticeable.