I would go for a 6 cylinder Renault Monasix Cabriolet Landaulet of ca 1928.It is indeed a larger car than the 6 cv models and it has the Renault hood lozenge of the later twenties .
Sorry pilou, but I didn't find any Cabriolet-Landaulet on Monasix chassis RY1.It seems Renault factory proposed only "Chassis nu, Torpedo 4 places , Conduite Interieure and Cabriolet Tous Temps..
It's not a Vivasix indeed, but by the trim level, it would be rather a Monastella (which is luxury version of Monasix) with specific Coupe Landaulet Body ==> Millon-Guillet? Binder? Kellner?...