Richie: first off dealing with KeenSignt will be easy for you, call Vicki and she will take care of you. Everything I have heard about the silicone is that it will work fine, if you are really concerned, they can utilize a screw set into your old bead hole to assist.Check out a somewhat radical example on their website, it is my Beretta 687 with a 1.5" rise on the existing rib.
Yes, you are right that as you lift the rib, if you don't taper it, you would adjust your POI, but my guess is that if 0.5" of POI makes a difference to you, you are a better shot and using a tighter pattern than anyone else on the site.
If you really are concerned about the POI, issue, just tell Vick, they seem to be able to calc. it out so there is not problem.
Mine works fine, you will like working with them.
Dennis Rinehart