Hi Misterbonkers
It's a requirement that the PC is normally conducted in the seat occupied for P1 functions.
I'm working from memory here so I can't quote the EASA regs exactly but I think you have added the words 'for P1 functions' yourself. The regs just say 'from the normally occupied seat' - that leaves things rather open for discussion. A co-pilot would normally occupy the left seat, a Captain would normally occupy the right seat, a TRI might normally spend more time in the left than the right so could normally occupy either seat.
We operate single pilot helicopters in both SP and MP role so as a matter of course, the initial SP LST is carried out in the RHS, the MP LST is usually carried out in the LHS; however, if the two tests are combined and are carried out in the RHS, the MP OPC is carried out in the LHS. Essentially, we try and cover every combination and permutation!
There is also a requirement to alternate OPCs between seats if the pilot is required to operate from either seat.
Hope that helps Geoffers.
TeeS