R6300v2 Slow throughput to internet

Hi there,

I am experiencing a similar issue to this post from 2018.
Router Model: R6300v2
Firmware Version: V1.0.4.52_10.0.93

Router is running in AP Mode.

The throughput on when using the internet port seems to max out at around 440Mbps, despite the port being connected at 1Gbps.
If I switch over to LAN, I can get over 900Mbps pretty consistently.

iperf via WAN:

[SUM]   0.00-4.00   sec   209 MBytes   438 Mbits/sec                  sender
[SUM]   0.00-4.00   sec   209 MBytes   438 Mbits/sec                  receiver

iperf via LAN:

[SUM]   0.00-10.00  sec  1.10 GBytes   943 Mbits/sec                  sender
[SUM]   0.00-10.00  sec  1.10 GBytes   943 Mbits/sec                  receiver

Anyone know how to improve the WAN throughput?

Thanks