Having had a good look over my heating circuit and rads, I've established that approx half the circuit is T'd off the main 22mm flow and return pipes (6 rads), then the flow and return have reducers down to 15mm and continue the circuit. The latter half serves 4 rads, which I've worked out to be approx 4.8kw in total output. Am I right in thinking the flow and return would better be 22mm all the way to the last rad?