More specifically: using heat loss coefficient (260 W/K + 880 W), output from my radiators (18 kW at ∆50) vs. the minimum output from my heat pump (4 kW), I can calculate the perfect weather compensation curve.
I’m pretty much stuck to a minimum flow temperature of 37°C, unless I’m willing to accept some moderate cycling (40 minutes on, 20 minutes off) which lets me drop to 33°C. So, another way of saying “improve performance by turning off the heat pump”.
(I set the thermostat higher during cheap Cosy periods, aiming to maximize heat production rather than efficiency, as this optimises the cost)