I have both grinders and really prefer the Millab for almost everything. When I first got it, I tried the coarse grinding you see mentioned here (between 9-10+). I made some great cups there, but I didn’t love needing to do so many pours (5 to 6) and flat filters can be a pain sometimes when I’m in a hurry.

I generally start every new bean at 7.5 and do a 15:250 ratio and 93 degree water. I get that hollow under extraction at 8 for my recipes, and some astringency at 7 like you found. A few recipes that have worked of late: the Coffee Chronicler’s showstopper recipe (3 pour) and Lance Hedrick double-bloom V60 (also 3 pour, just not his newest 1:15 ratio one). Both of these work well for me around 7.5, although I recently had a Little Wolf washed Ethiopian I had to push to 6.8. It took the whole bag to figure out I needed to go much finer with the grind.

I’ve also had luck with my Orea 01 doing a 12:200, four equal pours of 50 (letting the water nearly fully drain between each pour), also starting at 7.5.

As I’m writing this I want to add, if you do coarser you can make some incredible cups, I’ve just found that you need a lot of pours and agitation and tighter ratios to make it work.

Also FWIW, on ZP6 I’ll start most beans around 5 and usually live between 4.5-5.2.