@Kossie
I would recommend turning off 2.4GHz on Deco Main Network and re-running speed tests with 5GHz only. Dual band and band steering sometimes provide suboptimal results. After you've done with speed tests, if you need 2.4GHz band you can turn it back on.
In my tests with Deco M5, the best speed I ever got from Main Deco was 475Mbps, with average speed from speed tests in the range of 250-350Mbps. I could run two speed tests back to back and results may differ by 25% or more.
My Satellite Deco M5 delivers up to 225Mbps (at a peak) and less than that on average.
You should measure wireless speed by standing 1-2 meters away from the Deco, in direct sight of it and holding smartphone on the same level as Deco. 25 cm could be too close.
This is what my ISP recommends for placing WiFi mesh units, they call them pods:
- Space the pods evenly
Your pods work as a team, so they need to be close enough to communicate with one another. Try to space them evenly, no more than 10 to 14 meters apart.
- Install pods on interior walls
Ideally, place the pods along the interior walls separating the rooms rather than exterior walls.
- Keep the pods in the open
Wi-Fi signals travel through the air and generally weaken over distance, but their strength can also be affected by:
- Building materials: Concrete or metal make it harder for the Wi-Fi signal to move freely, ultimately slowing down your Internet speed.
- Appliances: Certain appliances, like microwaves or even baby monitors, can interfere with the Wi-Fi signal, possibly slowing down your speed.
- Ventilation: Pods should not be covered by furniture or placed in an electrical cabinet, where they can overheat and impact performance.