Hello! Welcome to the forum 
For other readers, this is a 12 kW split unit on 3-phase power.
What’s CoP did the system achieve over the entire year? Does this provide hot water too?
3.3 is okay, but there’s room for improvement depending on your climate. Manufacturer’s data quotes nominal CoP of 3.3 at 2°C outdoors with 35°C flow temperature:
You may be limited by the design of the heating system. The inclusion of a buffer tank and 5 (!) pumps has made for a complicated system which won’t be able to get great performance.
This might be addressed by balancing the radiators rather than increasing the speed of the pump. There are plenty of guides on how to do that, though it’s not as easy to do as they make out.
It’s probably best if all the circuits are pumped with the same flow rate. One way to determine this is to measure the difference in temperature (dT) between the flow and return, and fiddle the pump speeds until they match. However, I suspect that there’s only a little performance benefit to be gained from this, mostly by reducing the power consumed by the pumps.
Here are some other topics that may be useful reading: