looking at the specific requirements for the OP (ground sleeping , broader than 25" support required, some concern about thermal resistance and indirectly I would imagine a preference for a 2.5" thick mat..),I would think that the 9oz 1/4" thin wings plus 20" mat will not be much lighter , will be bulkier and most likely not as comfortable as a 30" mat.
The R value of 1/4" solid foam is about R1 (half of R2)