Preposition & hyphenated words

I just want to explain why my fixed-length contract is a contributing factor in/to my disinterest in the job.

1. Considering the bolded words, how are we meant to know what part of speech to use when describing another noun? Some appear to use an adjective; others a noun form.

2. I have a feeling I want to use the preposition 'to' because of the adjective contributing. But I think we use the preposition that works with the noun 'factor,' which just so happens to be 'in.' Is this the correct thinking?

3. I assume these use the preposition 'to', however?

a. I just want to explain why my fixed-length contract contributes to my disinterest in the job.

b. I just want to explain why my fixed-length contract is a contribution to my disinterest in the job.

Thanks.