I have a little jack like yours, but while I use it in the front, it's too small (too short a reach) to jack it up from beyond the rear bumper, so I use a 7,000 lb jack that has a long handle (that I can reach from well behind that bumper).

But my concern is, whatever jack saddle you or I have, with any metal saddle (and particularly one with a cup) we're really only applying lifting force at one or two tiny points where the saddle touches the differential.

My key suggestion is that I (and you should) use a block of wood perched on the jack's saddle, and use that between the saddle and the diff. Such blocks tend to spread the points of contact over a larger area, and being softer, doesn't stress the metal diff's housing as much.

Of course, a block makes the lift a little less stable, but after raising the car you're certainly going to finish off by stabilizing the lifted car with good jackstands, right?