I also have an 11 kW EcoDan, so I’ll add what I know about my system.
The EcoDan has it’s own temperature and flow sensors, so is theoretically able to estimate the COP based on those readings. They won’t have been calibrated though. It would be worth tracing where those sensors have been connected to the plumbing, and double-check they’re in the correct location. [see this thread]
I’d have expected the Sontex to have been wired into the EcoDan, so that Melcloud would report real, calibrate heat measurements. Assuming it’s been correctly configured that is.
There should be an electric meter somewhere nearby too, installed at the same time, also wired in. What are the kWh readings from both meters? That will give you another COP to compare. Possibly worth taking weekly readings for a while…
This sounds like it’s running well, except for the COP.
Looking at the MelCloud chart, the COP is way lower during the second year compared to the first. Something has changed with their system such that it is performing worse now. Have they had it serviced recently? Also note that the COP in the summer when only heating water is particularly poor, suggesting there’s an issue on the heatpump side rather than the heating side. The electric usage for hot water has also risen over the 2 years, so assuming that household consumption is the same, it is taking more energy to heat that water.