I finished the day by capitulating and installing an extra access point upstairs.

taf@bsd.network

The deck separating the two storeys of our flat is 25 cm of reinforced concrete and I just couldn't find a stairwell position that managed to cover everything in a reasonable way.

One @mikrotik wAP ax on each storey has me maxing out our outbound line from anywhere in the flat (yes, I know they're outdoor APs but the antenna radiation pattern and the ridiculously good value for money works for me).