last year i had 2 hot panels and two cold panels. The hot panels (not working properly) were the two on the inside, cooler ones were on both ends of parallel configuration. They are all the "sungrabber" models, a set of four 2x20 panels. my main concern is of cours maximum efficiency, but also whether or not i can use the panel that is missing the diverter (flow rate resrictor) in the header tube.

Last year i had this:
pump========
cold==================ll
warm=================ll
warm=================ll
cold==================ll
return========

I would like to repeat that all header pipes with diverter discs were at the return and pump side of this setup. We double checked that!