if the crown is covered with dirt it will rot
This is what the American Hemerocallis Society advises for planting daylilies.
"
•New plants should be planted about as deep as they grew originally. The original depth can be determined easily by the band of white at the base of the foliage which indicates the part of the plant which was underground.
•Do not set the crown (i.e., the point where foliage and roots join) more than 1 inch below the surface of the soil."
This diagram is from the A. H. S. website
I generally do not pay a lot of attention to the planting depth of daylily crowns in my location and growing conditions; they are probably nearly always at least a bit deeper than one inch (2.5 cm.).
Is the depth of the crown something that depends on whether one has hot humid summers versus cold winters?
