PMK Pyro and Delta 100

I just developed my first roll in pmk pyro, 120 format. EI of 80, standard development from G Hutchins charts. The highlights are wonderful, and the dark grays/blacks are very good. I have noticed increased grain in the midtones however. The grain is really only apparent on close inspection, not so much at a good viewing distance. Is there a way to decrease the apparent grain in those tones? I followed the development instructions as closely as possible, for tank development. Agitation was 5 vigorous inversions/15 seconds. There is no stain apparent to the naked eye in the non exposed portions of film (edges, between frames), but a good yellowish/brown stain in negatives.

I used distilled water for all steps, no prewash, water stop, TF4 fix, edwal lfn wetting agent, then 22 min final wash in tap water.