Your approach is the correct one.
There are other options such as using a free area load with an inclined surface, but that is unnecessarily complicated.
Shorter and clearer is possible:
lc 1
quad from 1 to 1 inc - type pxx p 0.10
= to = inc - type pyy p 0.11
= to = inc - type pzz p 0.12 or --
lc 2
quad from 1 to 1 inc - type pxx p 0.10; = to = inc - type pyy p 0.11; = to = inc - type pzz p 0.12
or –
lc 3
quad from 1 to 1 inc - type pxx,pyy,pzz p 0.10,0.11,0.12