Archer A7 has weaker WiFi signal with 21.02.0 compared to stock

I already expect that the A7 v5.0 will be slower with OpenWRT due to the lack of support for hardware accelerators (viz., Archer A7 has abnormally slow speeds on both Ethernet and Wi-Fi). I am okay with taking that hit to avoid proprietary software.

Unfortunately, the 5GHz WiFi signal is significantly weaker. In fact, it was so bad, that the connection was unusable and I had to swap the access point out for another A7 which still has the stock firmware. (Which works great).

Is there any explanation for this? How can choice of firmware affect the signal strength? The only thing I can think is that perhaps the A7 port of OpenWRT does not set the radio amplifier gain correctly, but that seems far fetched.