subgroup with 2 or 3 prefixes

Thanks from ttcf and others for answering:
1- In page 116 keys to soil taxonomy have Lithic Xeric Haplocalcids why we have not Xeric Lithic Haplocalcids
2- Lithic ustic torriorthent and aridic lithic ustorthent , lithic has 2 different places why? On the other hand in the first lithic is first prefix however in the later , lithic is the second prefix why ? what factors determine the position and preference of the prefix ?