When reviewing drainage structures in particular, I am seeing a significant number of structure with different materials on the inlet and outlet.
Since there is only one field, I recommend adding guidance in the assessment to determine with side of the crossing. That way there is some rationale when only one material is chosen.
Another option would be to create a new category: mixed, mismatched, etc.
Yes, the protocols from 2017 and 2018 state to use the dominant inlet condition to describe the material and shape of the structure, and add in the comments that the outlet is different.