Scouting out deals on solar panels for my 20' AGP, I notice that Fafco has a 'deluxe' model that has 2" headers, what do you make about the following company literature:

"Extra large 2in headers do not slow down your pool's circulation and insure excellent solar heat transfer to your pool's water. Because of the large 2 " headers, rarely is more than one panel needed for most above ground pools."

Does anyone take issue with that statement? Will the 2" headers really generate enough additional heat versus 1 1/2" headers to justify dropping a whole run? Part of me is skeptical that a 1/2" increase in header is enough to justify one 4'X20' run instead of 2.
I know more is always better with solar heat but is this claim legit? The 2" headers are roughly double the price of the 1 1/2" headers, Fafco claims that my pool needs 2 standard runs (4'X20') or 1 deluxe run.

I don't necessarily want to do this on the cheap, I'm not really interested in dropping a run of panels, I can fit 2 runs nicely on my roof, but if I still get 2 runs of the deluxe is that seriously like getting 4 runs of the non-deluxe, or is it just a wast of money? I'm skeptical.

The bigger headers provide a higher flow rate...and maybe some other things too. It seems unlikely that this alone would double the efficiency of the panel.

The 2" headers would let you save on pump electricity if you had a lot of panels, but they wouldn't affect your solar heating rate since that is a function of the panel size which is presumably the same 4' x 20' for each panel. For an in-ground larger pool with lots of panels, then I can see where the larger header size makes sense, but if getting only one or two panels for an above ground pool, then I don't think 2" vs. 1.5" header sizes make much of a difference. According to Fafco, a 20' AGP typically needs just one panel for heating, but since 4'x20' is only 80 square feet while a 20' round pool is a little over 300 square feet, you could use two panels for more heating if you plan to keep the pool on the warm side. I know for my in-ground pool I need panel area that approaches the pool surface area.

Note that their product specification says that the flow rate per panel should be 2-8 with 4 GPM recommended where the efficiency at 4 GPM is 80% and has a 2 foot head loss. This implies a bypass that is needed so only some of the circulatory flow will be going through the panels. You can see from the Installation Manual and this link that there is a valve in the middle of the header that directs some of the flow through the panel (the rest just goes through the header) so you adjust this per the instructions to get a specific PSI rise you can see at the filter.

Agreed, seems hard to believe that an extra 1/2" in the header could have such a dramatic affect, comparing prices I can't help but think that the standard panels are the better value at roughly half the price of the deluxe.