i beg to differ actually. bury the roots completely then pack the gravel/sand around the base. then very gently pull the plant upwards so you just expose the root crown by about 1cm. the reason for this is simple. the new leaves grow from the crown. if the crown is buried the first days of your new leaf are under ground and it will rot and die. in some cases the whole plant will die if the crown is buried too deeply.
when pulling out a leaf for pruning the base of the leaf should be a fleshy white colour, in a "buried too deeply" situation the leaf base will be a sludgy rotting brown colour.