The statement regarding the "smaller System A" doesn't mean that the Heat Exchanger is smaller, because it is not. System "A" has less fluid than the System"B" side. "B" holds 4.8 US gallons and "A" holds 7.2 US gallons of fluid.
System "A" pumps both electrical and engine driven are indentical and provide the same outpiuts. "B" system has bot more runing off of it, hence the larger reservoir. So maybe the fluid on the "D" side with the extra work gets a little hotter.