Staying Put arrangements

This is where a foster child can stay beyond 18, with a liability for rent that is covered by UC/housing costs for the young person. My question is how this income is taken for foster parents who are in receipt of benefits themselves. For UC, I wonder whether this would be understood as lodging income and therefore the bedroom would be treated as empty, but the additional income would be ignored?

I understand this can also be covered under section 23c of the children act which is ignored, however for this purpose, I want to understand the impact on means tested benefit entitlement.

Thoughts/experiences gratefully received