I agree with Variable load this is making a mountain out of a molehill.
The whole purpose of the OPC - be it JAR-OPS or EASA - is to establish the competence of pilot in role. The testing of handling competence in either seat should be undertaken in the most practical way. Normally (the exception when PICUS is being conducted), only captains are tested in both seats. That way a reasonable ratio of captains to co-pilots can be achieved to allow efficient flight and duty time allocation. The regulations were formulated to make this as easy as possible.
On two-crew helicopters, the roles of pilot flying and pilot monitoring are shared. These roles should be assigned to establish a fair sharing of flying and the safety of the operation. Where this is important - for example to a heliport where the landing surface is approached into wind and from the side with the best-field-of view - the roles might be swapped in flight at an appropriate time to allow a safe transition.
When not in training - be that type training, role training, line training or PICUS - command is allocated in accordance with procedures set out by the operator. In the absence of any specific instructions (for example for monitored approaches), the role of pilot flying or pilot monitoring is normally decided by the crew members on the day.
The days of the commander hogging the flying or making cross cockpit approaches should be well behind us.
Jim