DEACONLLB,
Yes, I think I understand what you are describing. I have only seen the pistol version of this rear sight and it does not look like it is satisfactory to use for a rifle rear sight because the aperture slot is too wide (too wide to obtain accuracy when one's eye is too close as with holding a rifle).
I have been looking for inexpensive alternatives to rework existing barrels into carbine barrels ~16+", either by cutting down longer barrels or by putting an extension (flash hider or compensator) on 15" pistol barrels so they can be used with a stock. The existing pistol sights won't work very well as a carbine rifle barrel. I don't like using scopes. Typical rifle rear open sights don't give a very good sight radius for a ~16" barrel.
My favorite type of sights are what I describe as diopter sights, maybe "annular" sights might be a better name, see image:
http://upload.wikimedia.org/wikipedia/commons/thumb/4/4d/Visierlinie.jpg/220px-Visierlinie.jpgI have a machinist friend who is going to try to mount a surplus front sight from an HK on one of my barrels. From making some estimates, I think that I will be able to match it up with a Williams style peep sight on the rear. I may need to use something larger like a ghost ring. I may also try mounting a surplus HK 91 or MP5 rear drum sight. Should be a fun project.