A gas turbine engine rotor assembly has a plurality of blades spaced apart from each other for rotation about an axis. Each of the blades includes a platform having an inner surface and an outer surface. The inner surfaces of adjacent platforms define a pocket having a radially outer wall, a pressure side wall, and a suction side wall. The pocket includes a leading edge wall portion and a trailing edge wall portion, and a shelf extending in a tangential direction relative to the axis from the pressure side of the pocket. The shelf is spaced apart from the radially outer wall.