The confusion is understandable because the pupil magnification (p) and its inverse (P=1/p) frequently are denoted by the "p" symbol in the equations. No wonder people mix these concepts, I have been known to do this myself and not only once.
Pupil magnification (p) is defined as the ratio: exit pupil/entrance pupil. Look into a telephoto lens from the front and you see a big opening, reverse the lens and the opening seems much smaller. Thus, a telephoto lens must have a pupil magnification (p) smaller than unity. (The opposite holds for a wide-angle lens).
So, the equation relating effective (Neff) to nominal f-number (N) is
Neff=N*(1+m*P) = N*(1+m/p)
where P>1 (and p<1) is a telephoto lens, P=1 (and p=1) is a symmetric(typically normal) lens and P<1 (and p>1) is a wide-angle lens
The rule-of-thumb is that the factor m/p increases much faster with a telephoto lens than with a wide-angle lens. Thus telephoto lenses don't lend themselves to really close-ups for this (and other) reason.
Finally, while we ponder the possibly deep implications of the equation above, the current AF Micro-Nikkors will effortlessly compute and display the correct Neff values all by themselves. No human intervention is needed, just interpretation.