Agree with arumgrande, isnbesondere the point stability. and would like to add the following thoughts:
Depending on the water retaining capacity of the substrate, the location (exposure to sunlight, the top layer, and of the pot and thus warming/evaporation rate) is just a mediocrity. I think that the layer not to fast should dry out ÃœBER of the Corm, so as to endanger the is forming roots by drying out.
By deeper plants it can be done in loose substrate. But since a sufficient depth is reached from 10-20 cm depending on the substrate safely.
You must think of the bulbous shape, for example longituberosus, pygmaeus, I plant so high it is just because the elongated tuber despite Palm pot otherwise winds on the ground (and maybe even there cancels).
I've had bad experiences with high potted plants in perlit-rich substrate, there you would have to implement larger vessels with low plants.
This year I was "normal" large containers with structure stable container for plant Earth and have planted relaitv high.
Because of bad weather, even the thin layers of the tubers dry hardly from, which is why the smaller plants now rain-protected inside are.
Open field may apply other laws: I have the information that someone plants his A. konjac 70 (!) cm deep and they resist the Frost this from another forum. They grow each year and are no longer ausgegeraben. Drive up the effort for the sheet so far by the Earth must be enormous. Whether small Cormels which I know do not really create. I sit a few middle and create just so...