How much mortar base

I have a Maax Studio 3 piece bath/shower with roof cap waiting to be installed. The directions are too general to be sure of proper installation. Specifically, the base of the tub rests on a sheet of wood which is supported by a wood "runner" and the front of the tub. The tub base has about a 2 inch clearance to the floor. The directions say to lay a mortar base before setting tub. Does that mean we goop it up between the tub base and the floor? If so, does the wood runner get set in the structolite as well? Not many of these have been installed in our rural area. Thanks for your input in advance.

The front apron would set on the floor,

The rest of the base can be supported by mortar.

I find it best to have a few lumps of mud that will squish out.

If you try to guess how much to put down and you lay it out solid, it could be too much and the base won't get down to the floor.

If the wood runner is in the air, it can be supported.