@Alexander12 we don't know what the orientation of the antennas in these devices is.

If you think about it though the field is probably a donut shape emanating horizontally from each antenna.

Some of the antennas will be at an angle, maybe as large as 45%, so the field is probably fairly good all round except for immediately below or above the device.

If you have devices on different floors I'd move them so they aren't directly above one another but also be aware of the distance between them and the effect that obstacles, like walls or floors, can have on wireless signal. It can be worse when they are not perpendicular to the wireless signal, eg. traversing through a wall at an angle will "look" thicker to the router than if if the traversal is perpendicular, and therefore can have an even greater affect on wireless signal quality.

  @raven-au 

Thank you for sharing your thoughts on wireless signal propagation. While those principles are certainly important to consider, I'm still encountering a specific issue with my Deco mesh network that I could use some help troubleshooting. Despite having one Deco unit connected via Ethernet, I'm experiencing internet access issues on the guest network. Have you encountered a similar situation before, or do you have any suggestions for resolving this particular problem? I appreciate your input!

  @Alexander12 Sorry, I haven't had problems like that. In fact I don't use the guest network.