Do you have any evidence to support this theory? When Le Cottage and L'Escapade offered 1:1 during slow season in the past, they didn't adjust their menu prices. Of the restaurants currently offering 1:1 for cash (Piazza Pascal, La Villa, Spiga, and Il Nettuno), I've compared their prices with their peers in Grand Case and found them to be mostly in line with each other (except for Spiga which has slightly higher prices).