Your pressure drop could be because of the bottle neck effect the smaller fittings have. Many of them actually reduce the inside diameter a little and therefore reduce your flow capacity, thus increasing back pressure. You can overcome this by having one more fitting than you thought. For example, I built a DIY solar heater and I used three half inch poly coils for a 1 and a half inch skimmer and return lines. Sound right doesn't it? Well the poly pipe nipples you must install to connect the poly pipe to the PVC actually are not a full 1/2"
so.... I added two more (just wanted more area and had the money and room.)
I would like to note that I only spent around $200 for my set up. This includes the plastic I covered them with to create a solar oven!!! It gets to 150 degrees in there!!! I have seen pool temp rise of 8 degrees in one day with 5 100' coils!!! If my calculations are correct that is only 125 sq ft heating a 24' round pool 8 degrees in one day!!! It was cloudy too and no pool cover.