Huh? I can't visualize that.
Put a plio box on the 24 inch side. Get on top of it on all fours. Put your hands on the floor about 16 inches from the box (or closer if you have the mobility), keeping your feet on the box. Then do what amounts to a hybrid between a horizontal regular ole pushup and a vertical hand stand pushup.
Great progression. My favourite instruction is: "You should not come crashing down on your head." It's not as if I would have a choice!