Cheap lifts?

I noticed that when I got mine I looked up concrete requirements for the same capacity lift from various manufacturers and their requirements varies greatly.
I have the manual for my lift and I don't remember numbers but I do remember them wanting more depth of concrete than other companies spec*d for theirs.
I've heard of cutting out either blocks or a whole rectangle bigger than the footprint of both posts and pouring a 3' deep pour/ and other lift companies saying specifically not to do that.
My garage floor varies from 5 to 6-1/2 thick with plenty of rebar, and an 18" square footer all the way around the perimeter. And at that I was worried about it being enough.