slab preprocessor on grade or in grade?

edit

Hi! I'm trying to model heat losses through the ground in E+. In the Auxiliary Programs document says:

3.4 Slab configuration Drawing The slab configuration used in the slab model is a “slab in grade” model. That is, the slab top surface is assumed level with the outside earth surface. If a “slab on grade” configuration, having the bottom surface of the slab level with the outside earth surface is desired, the best approximation is to use the horizontal insulation configuration.

I don't understand how a horizontal insulation configuration would help me if I want to model a slab on grade.

Also, in the utilities -> Slab in EquivalentSlab object there's a field named: "SLABDEPTH: Thikness of slab on grade" but in the field description it is said to be the thikness of the slab in grade.

Can you explain me which type of slab is modelled in the slab preprocessor and how I could model a sal on grade configuration?

Thanks!