I'd love to hear what you find out--this is from a simple experiment performed about a year ago because I had found the same phenomenon and was trying to pin down contrast. That said, I never ruled out reciprocity, but also didn't take the time to experiment further.

While you are right about the masking not making sense as a response to light intensity....there are many things that we have experimented with recently that haven't made too much sense. We're currently working on a new Carbon tissue and it's the opposite of what physics is telling us. Likewise, try adding more PT to a PT print and you get less contrast, less dynamic range, weaker blacks...but there's more metal!

Anyways, please let us know what you find. Hope you haven't froze your jiblets off already up there in the great white east.