How to place a mortar bed under an AFD Sterling Ensemble Vikrell tub

I’m not quite sure how to place a bed of mortar under this tub. It’s about 3 inches above the ground on the lower end and has 2 sets of these brace supports for “feet”. It does recommend a 1 to 2 inch bed of mortar. But I’d like to fully support the bottom with mortar. I just removed a majorly cracked tub and would like to avoid having the same happen again.

So far in all my searches I’ve only found advice for the tub that sits in the “little” feet. Any advice would be welcome. I’ve included a couple of pictures.