At the NATS college, all Simulation training is one to one so the course size shouldn't affect any course really. I suppose you could argue that a smaller course leads to instructors getting to know your problem areas more in depth and may be they could spend more time (ie more runs) with you specifically.
On the flip side, instructors will have differning opinions/styles on certain scenarios and it's good to hear and see different approaches to controlling and how they compare and contrast.
So the answer is no, the course size shouldn't affect pass rate
