"We may distinguish two main approaches to postulating these relationships. ('Postulating' because at the very beginning of a study we do not know which of the relationships are true, but we may postulate which of them may be true.)"
Are these sentences OK in academic writing? I would like them to: but am not sure whether this 'postulating'-clause is fine in this use, as it is a sentence fragment.
these relationships ('postulating' because at the very beginning... may be true).
I would remove the comma, de-capitalize "postulating", and put the full stop after the second bracket.
If you want to leave your original, it too is acceptable. The sentence in the brackets is a full and comprehensible one.