Simply pick the size hole that throws slightly more than you need; drill & tap a hole into that disk (from the side) so that you can screw a 1/4"-20 set screw into the hole making your own micro adjustable disc. I have done several and they work very well.
I would bet that trick works very well with Win 231. Very similar in theory to the adjustable charge bar.
Those smallest holes in the auto disks are long and narrow. The same is true of the adjustable charge bar when it is turned down to a very small opening. A powder with larger flakes, like Unique doesn't fit well in these long narrow spaces. A half height disk such as the micro disk somewhat addresses that problem by making the holes more evenly proportioned with regard to length versus width.
Still, your idea might help. I hate futzing with changing those disks!