Altitude selection will depend a little on how high above glide you are.
Just slightly above glide, set something below as a safety net. Normally no problem.
Glideslope WELL below will require a higher V/S, resulting in a fairly early altitude capture-phase of the FD, not really getting you close to the GS. So altitude selection above your current level simply works better, avoiding nuisance action of the auto flight system. But your safety net is gone....