Unfortunately, good old OMA is conveniently sparse of information, hence the search for an EASA definition. I’ve found a link to FTL questions to the CAA, so I’ll try that and report if any success.
another thing to remember is that, we pilots often get fixated on EASA regulations and OMA's completely forgetting that each country also have labor laws that also need to be adhered to. If the EASA/OMA is conveniently ambiguous to FTL, always worth checking with whoever is responsible for workforce/labor law protection in your specific country