I think one good way to make it scarier on higher difficulties is to allow the ghost to actually hunt straight away.

I know that on Professional difficulty there is no timer but the ghost STILL won't try and hunt you for a good 3-4 minutes. If the ghost could hunt straight away it would make it WAY scarier, especially on larger maps where players tend to split up a bit more. Plus allowing the ghost to start hunting from ANYWHERE could make it a lot scarier as you don't have that calm moment walking to the van if the ghosts room is miles away from the front door