I suspect uncooperative non-custodial parents is one of the reasons colleges keep the information vague, as it gives them the flexibility to do what they deem appropriate in any given situation. For example, one school told me they use the FAFSA EFC as the starting point (using custodial parent and stepparent) and then adjust only if the non-custodial household has significantly more assets and income than the custodial household. This means if the non-custodial parent is totally uncooperative they still have something to go on. If the custodial parent is getting child support, this is probably also a good indicator of the non-custodial parent’s income (the higher the income the higher the child support).
In principle, I don’t think the step-parents income should be counted, but I can see how this approach is also fair – it’s only taking into account one household and two parents, and reflects the lifestyle the student actually lives in.