To Dave M.--That's exactly it. The paper is blue sensitive, so the yellow-green filters out blue and pushes up the highlights, because the stain is proportional to the silver density. It also has something of a grain masking effect that is advantageous for enlargements.

I'm also using PMK for negs to be enlarged and ABC for negs to be contact printed on Azo. ABC produces grainier results but more contrast than PMK.