Thanks - very interesting. You are achieving better performance than me at higher flow temperatures! I don’t think 4051 will do anything for me as I don’t have a PWM pump.
From this thread Oversized ASHP (Samsung), flow rates, LWT and dT, it looks like the way Joule systems are plumbed with some 22m pipework means they are restricted in the flow rates they can achieve.
I’m coming to the conclusion that I need to prioritise balancing the radiators to get the dT to 5, and see where I go from there.