In a message dated 97-12-14 17:25:14 EST, sterman@sprynet.com writes:

I don't get it.  Must be some kind of weird time/space distortion Star 
 Trek field thingy.  Ranma must grow about four inches whenever she 
 approaches Akane.  When they separate, Ranma shrinks.
 
 Or it could be RT, either consciously or subconsciously, is making the 
 point that Ranma is still the "man" of the relationship, so must always 
 be taller.  I grant this is perhaps reading too much into it.
 
 Anyone else observed this?  Any other theories?
 

I have a theory. It's the Mysterious Expanding P-chan Effect. 

Notice that P-chan shrinks and grows erratically, in both the manga and the
anime. I can't think of a manga example offhand, so I'll use one from the
anime: In many appearances of P-chan, you see him being cuddled and fed by
Akane. He's quite tiny, able to be held in one arm. 

HOWEVER...

Watch "Team Ranma vs. The Legendary Phoenix", when Ranma-chan goes into the
bath. At first, P-chan is small enough to be seen trotting alongside her foot.
However, when Kunou charges into the bath, P-chan jumps onto Ranma...and
manages to cover her breast while hanging from her shoulder.

The same effect seems to be applying to Ranma-chan in the manga. ^_^

-Lurker