I'm going to be installing a pair of Vespin II toilets.
The floor is concrete slab, and I am using a porcelain tile on the floor.
I have cut out a circle in the tile so I can drop the tile over the flange in the floor.
My question is whether or not I have to use a riser/adapter.
The paperwork with the Vespin suggests that I do. But I put the unifit over the flange (without wax ring) and I don't think it will be necessary.

How high can the tile be before you need this adapter to raise it up?
Thanks!