Getting those sensors fitted better will likely make a big difference. 
The heat pump will run the primary pump (grundfos?) at a fixed speed (5 in settings), and the flow rate (10 l/min) will be the result of that setting. Reducing the speed will increase the dT between flow and return. This doesn’t influence COP much, but will mean slightly less power going to the pump. Errors in the heat calculation might also be smaller as a result.
The second pump (wilco?) will be circulating the hot water out of the buffer to the radiators. The optimal configuration would be to match the flow rate of the radiator circuit to the that of the primary circuit. This is a bit of a faff to do, and needs either a second flow meter, or measuring the temperature at the 4 ports of the buffer. Some details in this topic, though probably not worth putting much effort.