I've seen an evo stuck in a case that claims only 152mm clearance. The cooler had 1mm of space left. It's one of those things where there is no standard by which it's measured. Some are measured to a solid side panel, given an extra 5mm or so, and that supposedly includes all models, not realizing there's an extra 4mm in the tempered glass side model, and -4mm for the acrylic side. But they'll claim the same measurements anyways. Technically correct, there'll be 1mm, 5mm or 9mm extra clearance, but nobody changes, remeasures, updates web info, just on a panel change. And you'll not know what's what until you try.
Many times, the specification is taken as a measurement of the side panel perfectly straight, so clearance is removed to cover flex or warping of the panel that's common during manufacturing process, user handling etc. Meaning with a perfectly straight panel, there's really 163mm of cooler clearance, but warpage of a fitted panel might go upto 5mm on the center, so cooler height is stated as 158mm
No standard, every manufacturer is different, and there's no telling what those design engineers figured into the equation.