While we don’t have validated test results to share yet, I’m fairly confident you should be able to achieve 10 meters or more for a point-to-point connection over Thread. For a point of reference, Nest’s latest product Nest Secure is a security system that uses Thread for communication between the motion sensors (Detect) and control pad (Guard.) According to their FAQs Detects can be up to 50 feet away from a Guard. And that’s in indoor conditions, with wires and metal in the walls and your use case appears to be more ideal.
Based on your diagram it looks like the green boxes are all acting as endpoints but it is worth calling out that if some of those were repeaters (solar?,) the effective range from one corner of the network to the other would increase by taking advantage of the mesh.