I don't know Norcros adhesives, and I'm never likely to, but in my experience the maximum bed depth of an adhesive will relate to small isolated areas and not the whole install.
It could well be cheaper to use a board or latex to make up the deficit.
I'd probably go with latex, to obtain a perfectly level substrate.
Completely agree with @3_fall plus with heavy stone, bulking out 10mm of addy you would undoubtedly result in some slumping issues as it dries