In the procedure design, it is assumed that there is 5.8m from the ILS ooglidepath to the lowest part of the wheel path. I wont even consider eye path i or not coincident with VASI.
Currently, with the larger aircraft, and the stretched versions, this difference is more than 5.8m (ie A330/340 is 8.1m, A350-900 is also 8.1m)
When looking at operations, to assure obstacle clearance and aiming point, it is important to know the RDH, and the foundation, so that the operator calculations of ARDH and have sufficient clearance at the threshold, especially for CAT II and III procedures.