My thanks to recent responders.
A little more search has bolstered my newbie-confidence about click dome sizes. For open and closed, I’m now fairly sure availability is 10, 8, 6mm for closed and 10, 8, 4mm for open for Sivantos products.
This discussion & search soon became TMI (too much information). If interested, see below.
Nov 2016 Signia Product Brochure
Spring 2017 Government Services pocket guide (by Signia)
Just found a user comment in another thread about cutting the open domes to allow better fit.
[Quote]The soft cone that goes into the ear has circular design that if you cut the spacing support around the base of the cone, this action reduces the pressure from the outer rim of the cone on the inner ear and makes wearing them much more comfortable. The cone still fits snug in the ear and sound performance isn’t affected. You can cut the spacing between each rib one at a time testing after each cut. Your not removing any material with each cut. Your just allowing the outer circle of the cone to compress easier in you ear canal making it more comfortable in your ear. [End Quote]
And, a technical Signia article on fitting Click sleeves (vented and unvented) with open dome and double dome comparisons in RIC applications.