I have two methods I use. The first is much like yours except I use only coarse river sand in a very shallow pot/container, put under shade cloth and await roots.
The second; I dust the cut area once dry with rooting powder (not gel) and sit it on top of a tube like pot of similar size, make sure you get a good coating of powder. Ensure the pot does not have too many holes or it will not be dark enough to encourage rooting. Again place under shade cloth and await roots.
Both work pretty well but I still have trouble with Ariocarpus and Asterias degrafts. They are hit and miss. I have good success with Myriostigma using the first method.
Goodluck
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