What is the link speed reported if you have a HP Windows laptop?
Example:
I don't have 500mb internet and I am not able to test OEM or openwrt on my sole 'live' R4A which runs Padavan in AP client (wireless bridge) mode.
I however, did briefly reconfigure the R4A to act as a simple AP and use iperf3 server running on ethernet wired Windows desktop PC (192.168.10.11), and iperf3 client (below) running on old laptop.
Laptop with Intel 2x2 AC wifi card about 1m from the R4A.
Link speed flipping between 780 and 866 Mbps
Router reports 867 Mbps
Each test only executed ONCE.
AP mode:
Multi-stream download
iperf3 -c 192.168.10.11 -t 10 P 6 -R
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-10.00 sec 368 MBytes **309 Mbits/sec** receiver
Multi-stream upload
192.168.10.11 -t 10 P 6
[ 4] 0.00-10.00 sec 329 MBytes **276 Mbits/sec** receiver
single-stream download
192.168.10.11 -t 10 -R
[ 4] 0.00-10.00 sec 402 MBytes **337 Mbits/sec** receiver
single-stream upload
192.168.10.11 -t 10
[ 4] 0.00-10.00 sec 334 MBytes **280 Mbits/sec** receiver
before I returned the R4A to its original function as a Wireless Bridge where I see iperf3 speeds (267-400 Mbps) when wirelessly linked to Asus AC1900 router (OEM firmware).
If it means anything, here are results from my Mi 4A Gigabit in AP mode, 5GHz only (2.4GHz radio disabled), with txpower 14, iperf from router to workstation equipped with Intel Wireless-AC 9260 reports 650-866Mbps while router shows between 520 and 550Mbps:
$ iperf3 -c workstation.lan -t 10 P 6 -R
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.01 sec 370 MBytes 310 Mbits/sec 0 sender
$ iperf3 -c workstation.lan -t 10 P 6
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.00 sec 201 MBytes 168 Mbits/sec 542 sender
$ iperf3 -c workstation.lan -t 10 -R
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.01 sec 382 MBytes 320 Mbits/sec 0 sender
$ iperf3 -c workstation.lan -t 10
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.01 sec 179 MBytes 150 Mbits/sec 113 sender
My config is almost the same as the one from first post however I have disassoc_low_ack enabled