I had to go check...I'm at 16 stitches per inch...1.8 on my Janome 6600.
I think for piecing you want your stitches short enough that they don't fall apart
when pressing/handling but long enough that you can unstitch if you have to.
I also don't backstitch for piecing (contrary to garment sewing) thus I prefer the
shortest stitch I can manage.