This comes up quite often where Mazda have broken with convention and given a capacity rather than fill until full.
The rear diff on the new model is equipped with very low friction ball bearings which reduce drag and the oil is this SG1 high tech synthetic stuff. The capacity for you guys is shown as 3.7-3.1 qts and it doesnt matter that it doesnt reach the level plug. They have done all their development work with that amount of oil in and the quantity added in the works is very precisely controlled just like every single bottle of Heinz ketchup. If they underfill, they are breaking the law and if they overfill by one drop it costs a fortune. You can back the car onto a ramp and when changing the oil, just add the specified amount and it doesnt matter that it is leaning forward, just put the plug in and go. It will not reach the level plug.