Spot elevation placement

You want to control the placement of your spot elevation, either on the top of the slab or the bottom of the slab.

Solution

Spot elevations will be placed on slabs in different locations depending on your view setting. 
In wireframe view, the slab cannot be seen. As a result, spot elevations snap to the bottom elevation of the slab where the topography has been cut out.
If you change the view to hidden line view, the topography below the slab cannot be seen. Only the top of the slab can be seen, so the spot elevation snaps to that.