Factory the lower sits on top of the spindle. EKMW kit used to say 24-28, now it says 22-28. I measured and from top of upper to bottom of lower there is 16.5". I should have no problem running factory 20s on the EKMW kit.
thats not how you measure it, but evidently it works on the NNBS. you measure from center of the hub to bottom of the lower ball joint.
for instance, on NBS trucks with the Ekstensive kit and stock spindles, that distance is ~9.5". if you take a 20" wheels and subtract just 1/4" for wheel thickness, you only have 1/4" clearance at the most. tire size, wheel make, and design will all play a part in it.