Wireguard upload is faster than download

I have a TP-Link Archer C7 v2 running openwrt 22.03.5.

In my Wireguard configuration, the MTU is set to 1420 in both openwrt and its peer (pfsense).
My WAN is 100/100 which I have confirmed using speedtest.net. The upload and download speed are nearly the same.

However when I run a iperf3, upload speed is around 60MBit/s while download speed is just 30MBit/s.
Results are the same when I switch the role of iperf3 server/client.

Are there any areas or tweaking that I can look into to brush up the download speed?

Thanks in advance for any suggestion.

Are you running iperf3 on the router?

If so iperf3 is very CPU intensive and can skew results if it is run on the router.

For good comparison run iperf3 on a local LAN client

Yes the iperf3 tests were done in router. But connected devices show similar results. In particular, download speed is about half of the upload speed.