All local contrast adjustment does is compensate (somewhat) for lower resolution/detail per print area inherent to larger print size. That is an entirely separate issue from actual colors changing from small print to large...
Gotta disagree there.
There are significant perceptual differences for color and tone imposed by changes in scale. I first noticed this, oddly enough, way back when I built scale models of airplanes and tanks. (Yes, I was a dork. Went with being a history major.) You could pick the precisely correct paint color for a given subject, an exact match for the real thing, yet when you looked at your completed 1:35 scale model the color looked very obviously too dark. This perceptual problem is well understood by experienced modelers, who end up lightening the paint colors by an amount determined by trial and error to get something that looks right. There are also differences in shadow vs. highlight perception imposed by scale. Larger subjects tend to have perceptually more 'open' shadows; there's enough light bouncing around that we can see into the shadow areas more easily than with smaller subjects. It's true for both prints and 3-dimensional objects. That's why for larger prints you may want to darken the shadows a bit to get back to the same
perceived tonal balance.
John Paul Caponigro's bit about adjusting tonality for the scale of the print is addressing exactly this issue. It's a perceptual quirk of human vision, not a principle of physics, so there's no way to measure it. You can measure precisely the same density in the shadows of a large print or a small one with your spectrophotometer; but they will
look different to your eye because of the effect of scale on perception. Caponigro's rule of thumb (darken the print with a curves adjustment by 1% at the midpoint for every doubling of print area) generally gets you close; after that it's "season to taste".
