[pHaestus]

Well from my standpoint the size of hose is a sort of non-issue. It is, to me, one of the design parameters that affect pump choice and not much more. The "American" approach to systems evolved around what was readily available for DIYers and mostly empirical observations. My exposure to the "German" approach is limited to when the Innovatek kits were released a couple of years ago. Even now I am mostly familiar with European mfgrs as providing "complete kits" where US water coolers treat mfgrs more as "wb makers" and assemble the rest themselves from auto stores and pet shops. There is good and bad with this; a sense of satisfaction and accomplishment come from DIY but presumably an engineer can assemble an optimized matched kit that gets the most out of all the components chosen.