TLDR:
Any ideas how to properly setup WiFi roaming between two different WiFi routers in a single floor flat/apartment?

Also anyone know if just configuring Mobility Domains in each router would help? or is mobility domain specific to 802.11r[oaming?] (which does not seem to be implemented even on advanced-customer products).

---

Currently I have Turris Omnia (which has customized OpenWRT) as the primary router (DHCP, firewall, etc) and basic TP-Link Archer C6, both dual-band.

Direct line both are rather close to each other but with walls between them. TP-Link is in the furthest/farthest? room, Turris basically a bit off the center of the space, so there is some overlap of signals and I’ve hoped that the devices would sort it out, but with that it seemed to happen too late - especially androids tried to really hold onto the basically dead wifi for too long.

With this setup I’ve tried the basic “roaming” configuration:

• Same SSID
• Same encryption and PSK
• Different channels (for each band, per router, bo)
• Even tried tweaking the signal powers for each so that there is less overlap (reducing power of Archer so that it mostly covers only the farthest room)

But, either tp-link does something extra under the hood which breaks this or the routers are just too close to each other and it does not trigger switching in the client devices (androids, iphones, macbooks, thinkpads).
Also with both routers on the same SSID, it was hard to forcefully tell the devices to connect to the other WiFi thats like almost next to you instead of staying on the previous dying one.

I could replace the cheap basic Archer C6 with capable Mikrotik to get more control and try setup the Mobility Domain but I have no idea how it works and if it even helps with roaming.
One earlier web search hinted that for the usual “roaming”, all the broadcasted networks have to be in the same 802.11 mode (N vs AC) for devices to even consider roaming (as in, they like to stick with AC even if there is N network with better signal).