If the heatercores are each in parallel to each other, then you get a reduction in the resistance compared to a single heater core, and hence an increase in flow rate.
The reason is that the PQ is typically some function of the velocity of the water, which is some linear function to the flow rate. Example is the MCR120QP, which I calculate the head (in meters of water) as being:
0.021*Flow*Flow + 0.015*Flow
where Flow is the flow rate in litres per minute.
Now, place two radiators in parallel, and you halve the flow rate through each. Take that MCR120QP and put 4 LPM through it and I get 0.4m of head. Put only 2 LPM through two rads in parallel, and both present only 0.11m of head. Put four in parallel and you get 1 LPM through each and only 0.04m of head.
However, you get increased restriction from both the tubing linking them up, and also the intersections (maninfolds, Y's, T's whatever). Even so, the overall flow rate is typically superior in a parallel setup.
Tragically, performance is typically NOT superior. Each radiator is getting a flow rate far lower than the overall flow rate. This reduces turbulence and mixing, and reduces the effectiveness of the radiator. Sure, its not much of an effect (see yellow line on Graph 11 here:
http://thermal-management-testing.com/ThermoChill.htm) but its present.
In the end, radiators are all about getting maximum air to metal contact to cool the coolant. More air and cooler air equals better performance. Sharing one fan between four radiators will be rather detrimental to performance. You're getting close to a passive setup and should expect similar temps (and, to your benefit, similar noise).