@AlexS_in_S

Can you clarify how would you want to see them connected? Patio to Lounge or Lounge to Patio?

  @Alexandre. Thank you. Indeed for me it would make more sense thatcher line is kitchen to lounge and lounge to patio. It is actually in line from a positioning point of view with a clear line of sight. While kitchen to lounge is 5 meters, lounge to patio is 4 meters. Why should kitchen bridge 9 meters to serve the patio, when lounge could/should do that? Can this be programmed or set up? Thanks again. Alex. 

  @AlexS_in_SA 

By default, Satellite Deco prefers connection to Main Deco. TP-Link gets a lot of questions on that design decision, so they did create FAQ article: Why does the satellite Deco still keep selecting the main Deco as a signal source instead of another satellite Deco?

In your case, both Satellite Deco show excellent WiFi signal to Main Deco. If you connect Patio to Lounge instead of Main Deco, WiFi speed on devices connected to Patio will be half of WiFi speed on devices connected to Lounge, because of extra WiFi hop.

Some people find this explanation unsatisfactory, and in some cases (not yours) that design decision does not work well. TP-Link started to introduce Connection Preference feature described here: How to select a preferred signal source on the Deco App

Check Deco app and see if that option is there. If you do not see that option in Deco app, your M4 does not support it. There might be beta firmware available, but as long as you are otherwise happy with Deco mesh performance I would not recommend installing beta firmware.

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>I also see, that devices are not connected to the most logical deco, meaning not the nearest deco a device is connected to. 

As for devices, they do not necessarily connect to the nearest Deco. They do not know which Deco is the nearest by distance. Usually, their connection algorithm works like this: find WiFi mesh node with good enough signal, connect to it. "Good enough" is left for software developer to decide and could be different between different devices.

When you have multiple Deco nodes in reasonably close proximity to each other, device will scan WiFi network until it finds first with "good enough" WiFi signal. Device will connect to it.

Also, I suggest to give it about 24 hours for device connections to settle down. Do not restart Deco mesh or individual Deco units during that time. Some devices might move to nearest Deco in that time frame. Those that don't, as long as they have good WiFi link and show no issues connecting to whatever Deco they want to, just let them be.

I, for example, have HD/4K quality security camera from TP-Link that likes to jump between all four Deco nodes I have on three floors. It keeps streaming in maximum quality it could anywhere it is connected, so I decided I don't care where it is connected.

On the other hand, Smart Plugs I have from TP-Link, that transfer almost 0 data, migrate to their nearby Deco units in 12-24 hours. Go figure.

  @Alexandre. You are super. Thank you so much. All makes sense to me. Thanks. 
The question about the devices connected has the  background, that some of my smart devices like smart timers for geyser, pool pump etc. have reported weak WiFi connection. And they still do although massive upgrade with the Decos, coming from a regular router. In any case, I will may move the decos around and test it out a bit. 
 

Again, thanks to you and your friendly and professional answers and insight. 
 

Alex.