The CAA can act to give freedoms as they see fit. After all if one is acting in accordance with CAA guidance why should you fall foul of any regulation afterwards? The scenario you paint seems entirely reasonable and [without knowing the restricted instructor experience] perhaps the supervisory element means what exactly in terms of value add. The interesting piece will be the cross country navigation part. Although surely the easiest starting point is the supervising FI?? He must have clarity of where he got his guidance from?