The actual difference between an offset and a rectangular cantilever umbrella lies in the design of their poles. First of all, unlike with traditional umbrellas, they’re both on the side rather than in the middle.
However, in an offset umbrella, it bends at an abrupt angle over the shaded area, with the canopy attached to its end.
With a rectangular cantilever umbrella, there’s another piece attached to the main pole to keep the canopy suspended and offer more positions and angle possibilities.