I know this is trivial but still worth maybe doing. Currently to achieve full bars in OpenWRT you need -57 dBm or better. I feel like this is asking too much where the normal user might think there is a problem.
After reading this: https://dongknows.com/wi-fi-signal-strength-dbm-explained/
I think it generally makes sense to move this value to maybe -60 dBm or better for 4 bars. That's slightly more realistic for most people.