That gives a flow rate of 21LPM and a boiler output of 23kw, also the mid point (mean) temp of each rad is remarkably consistent at ~ 62/63c and probably pretty accurate as the mean of the boiler flow&return is 63C, giving a rads output of ~ 84%, don't see any real reason to balance these rads based on your numbers. 18C is a almost perfect dT IMO. You might just take another cycle time after full system heat up as difficult to see your hose requiring 23kw to maintain 19/20C.