Radak is not a good analogy because it's a stand-alone. It seems likely that Hatam is in semikhut with Sofer. Why wouldn't it be? Furthermore, Orthodox Ashkenazim pronounce his name Chasam Sofer. If there were a kamats under the het and tav it would be Chosom.
Barry Barry Dov Walfish, Ph.D. Judaica Specialist University of Toronto Libraries Toronto, ON M5S 1A5 Canada