Test results from
@limcc using RT-AX86U for reference (Post 3026 and Post and 3027) to show it is quite possible to cover a typical 4-room/5-room HDB flat using single router. In the same page, there are also reports of ZenWiFi Pro ET12 with 5GHz/6GHz comparison from another user.
Each flat is not the same and sometimes it is not possible to place the main router in an ideal central location of the flat. In that case, those with LAN ports in the rooms will be much easier to add an AP to compensate. Those without LAN ports in the rooms may have to go with more expensive triband solution if they do not like to lay Ethernet cables.
https://forums.hardwarezone.com.sg/...400-rt-ax5400-and-tuf-ax4200.6315347/page-152
I envy them. I think it may because of the kind of walls I have. Mine is an old flat, built about 30 years ago. It’s a EA, the old type of EA, so a bit bigger and probably tougher walls.
I can’t move the main router because of the design of the house. It would be ideal to place it just outside the study room which would be the center of the house but just not practical for me because I don’t have any fixture at the spot to put the router.
Anyway I spent the whole day playing with the Asus settings: updating the firmware, turning AiProtection on and off and testing speed, turning UPNP on and off and testing speed, turning remote access on and off, turning QoS on and off, turning VPN (WireGuard) on and off, but it didn’t help the speed, nor did it help with the range to the MBR.
Actually each time I make a change in setting, it takes a while, nearly 2 minutes to take effect. All the changes add up, so it took a long time fiddling with all the settings. And when I did firmware upgrade or change from Smart Connect to disabling it, it can take 6-8 minutes. Pengsan

. Honestly my old Linksys AC2600 was faster when I made changes.
But the good thing is that I managed to reconnect my Synology NAS. Had to change the IP address but was relieved that it connected. And also reconnected all my Starhub TVs.
So no choice, I went out and got a RT-AX57 and made it a mesh node in the MBR. Got it for $79 at Cash Converter. Updated the firmware. And got it wired backhaul to the AX89X.
I then tried to use Smart Connect and set both the 2.4/5GHz bands to the same SSID and let the router does the band steering. Was hoping I could get the seamless roaming handoff I wanted.
But I had a hard time getting Smart Connect to work. The connection keeps dropping! Then I disabled Smart Connect and set up separate SSIDs for the 2 bands. Still got problem! The 2.4GHz band will connect and stay connected but the 5GHz band will not!!!!

Kept dropping off.
Then I tried to change the password to see if it helps. Good grief. After changing the password back and forth, even copying it to paste into the iPhone WiFi connection, I kept getting a new error that the password is wrong!! Very xian already.
Finally, I think I found the problem. Can’t be sure it is the real cause but the solution worked. I don’t know why though. It’s the 160 MHz bandwidth under the 5GHz band. When I disabled this 160MHz bandwidth, voila!, all the stars finally aligned. I got the Smart Connect to work, got the seamless roaming to work, and no more dropping connection.
The speed - with the AX57 node installed - was decent. The speed test in the Asus app gave me readings around 970 Mbps whereas the standalone Ookla Speedtest app gave me only 300-400 Mbps. Don’t know why.
Anyway, if I’m using the laptop in the bedrooms, I will use LAN and not WiFi.
Tomorrow I will get another two more AX57 and fix up the other two rooms.
This is the end of my quest to fix up a Asus mesh in my EA home. Quite a journey. I learned a lot about MIMO, routers, nodes, antennas etc. in the process. Quite useful.
And thanks to everyone here for your advice and help, especially
@xiaofan! Much appreciated!