American Standard Mod. 2425 L Install

hey guys,
i just brought my tub home and after reading the instructions i have a couple of questions.
1. how large of an area does the mortar base need to be?
the instruction say the entire tub base needs to be supported but does give you an idea how large to make the mortar base.
2. How deep does the mortar base need to be to make good contact with the bottom of the tub?

any other inputs or advise would be GREATLY appreciated>
Thanks

If you use mortar under the tub, I like to keep the gap about an inch between the floor and base of the tub.

Then I put a few small piles of mortar down and quickly drop the tub, squishing the piles out some.

The worst thing is to try to lay mortar evenly, and then find that it is so solid that the tub won't drop down into it.