Composite or Single-Field Clustering Key
This is bollocks:


  ... ClaimId alone is a better clustered key because it is narrower


because of this


  ClaimId alone is NOT uniquej


A non-unique clustered index will add a 4 byte uniquifier to remove ambiguity of ClaimId because it is the clustered index. Why? One reason is all NC indexes refer to it: so how to know ClaimId is which?

It was demonstrated (some time ago, maybe not valid now and can't find it) that non-unique clustered indexes break when you exhaust 2^32 values of the 4 byte uniquifier 

Edit :

Question states ClaimId is not unique so assumed that uniqifier exists. No need to comment that it may not exist in the context of the question