Hey guys, thanks for weighing in on this.
The more I've thought about it the more I think the whole(?) phenomenon can be explained with reciprocity failure. Each successively more dense part of a negative is going to experience more 'reciprocity failure', and if the overall intensity of light is reduced this effect will be exaggerated throughout the scale of densities (thus, more contrast).
The masking explanation doesn't make sense to me... and that's not to say it's wrong, but I just can't reason it out myself. My thinking is that the printed out silver which constitutes a mask is going to be formed at the exact moment the silver-chloride achieves enough exposure and that's that. You can't sneak in any silver ahead of, or behind exposure. The mask is built up gradually just like the exposure is; in fact it's created in direct proportion to exposure, it is after all our only evidence of exposure. This doesn't belie the reciprocity failure explanation (the disproportionate relationship of light to exposure). It's impossible however, for exposure and deposited silver to diverge from one another, they're 1 in the same, and if that's the case, how can the masking have an effect on contrast between 2 different exposures of the same negative?
Though... Klanmeister... that's an interesting caveat... it does kind of make sense how an initial intense exposure could set you up for a given contrast, because this would lay down a mask which doesn't show the effects of reciprocity, and that would undoubtedly have an effect on the subsequent printing. Hmmmm...
The plot thickens!
What do you guys think?