I must be missing something, because I don't see how you make a shroud chainplate adjustment that's "less than 1/2 of a hole
It's obvious to someone who has been doing it for years, of course.
I'll call the part of the adjuster attached to the shroud the shroud tang, and the other part of the adjuster the vernier plate.
A "full hole" adjustment is defined as removing the pin , then moving the hole the pin was in on the shroud tang to the next open hole on the vernier plate, that is to say the hole the pin was just in slides down to the next open hole.
The trick with these adjusters is that the holes are not evenly spaced, so before you get that original hole slid down to the next open hole, you will see a bunch of the other holes lining up with different holes along the way. This gives you the possibility of less than the "full hole" motion described. A full hole of motion is a lot of tension, so you need the "less than full hole" to get the rigging right.