FINAL UPDATE
As there was direct sunlight here this afternoon, I could expose again both sunny and soft scenes. This new development is right: I mean both types of scenes mixed for a single development time can be wet printed without dodging or burning, just the way film was designed to work, in my case using filters 3 and 3 1/2 for soft light, and filters 1/2 and 1 for direct sunlight.
It was fresh current TX@640, Microphen Stock 21C, no presoak, 6 minutes, 2 slow inversions in the beginning, 1 slow inversion at minute 2, and 1 slow inversion at minute 4. Stop bath at minute 6 (I preferred to use stop being stock), fix, rinse. Condenser enlarger.
WHAT I SEE
I got the same small grain again, and I don't think it's just because of the shorter development time: I agree with Erik van Straten... Different lenses can produce different grain sometimes. Possibly grain is lower in my case because of the low contrast lens, though I think I remember he said he liked the small grain given by his 50 2.5 Voigtlander Skopar, a modern lens. Maybe other lenses he owns (current Leica 50's) are higher contrast... Anyway, my first (over)development today showed a lot more contrast, and not only more grain. So grain grows quickly when we develop for the longer times required for pushing. On the contrary, it seems low contrast native speed developments with Microphen produce a lot less grain than its more common use for uprating, and this makes it a great developer IMO because it can be well used in most (and very different) situations, instead of using two developers. Now I have no problem in using Microphen for the box speed range. It also echoes what Lex Jenkins said about TMX at box speed in Microphen: as good as D-76, but better tone at EI100 without more grain.
WHAT I WASN'T EXPECTING
I thought Stock was going to produce less grain than 1+1, or at least that it was going to dissolve it a little more: not at all. I see what Ian Grant means when he talks about the sulphite being dropped in Microphen design. With Stock solution Microphen Tri-X has grain that's equally small, equally tight, and equally brutally sharp: I see no difference with 1+1, so I'll never use stock again for the box speed range, only for 1600 in those unusual low light situations. I imagine being "only" 640 this case, occasional mixed sunny scenes can also benefit from 1+1 to help avoid blocked highlights as Microphen stock is very strong even when we seldom agitate.
That's all, bye.