While aperture (peep) sights are designed to be mounted on the receiver or tang with relative closeness to the shooter's eye, open sights would have to have the tiniest of notches to work. If an UltraLux sight was mounted on the receiver, there would be a huge amount of open space on each side of the front post in the sight picture. Precision shooting would be most difficult.
Also, please note how the sight radius varies among the Special, FS, and UltraLux in my post above. We shoot several casual sporter matches at my local club and several shooters use all or some of these same three rifles in the matches. It is interesting how each shooters individual eyesight draws them to one sight radius more than the others. In other words, it depends.