Doesn't matter what direction the z axis goes, usually it will go up and down during a print unless you aren't using a bed mesh or z hop. Just because its in a printer assembly manual doesn't mean its right. For example the common 130hz at 150mm of free belt length is the norm for belt tightening procedure, in reality its undertightened according to the belts manual. The drag chains used in voron are way to small, the drag chain manuals basically say that all wire must be arranged next to each other, not so densely packed as they are. Meanwell uhp manual ask for the psu to be installed on a large aluminium plate, size depends on psu size, with thermal compound as the uhp series of psus are only so small because they rely on external heatsinks to stay cool enough under continuous high loads. Meanwhile people bolt printed clips onto them and install them onto din rails. Not to mention the use of smooth idlers or bearing stacks on the teethed side of the belts. As you can see, the 3dp community is excellent at ignoring installation manuals from the companies making the stuff