I think Bellamy understood about modes, he sang with young tradition, and was very experienced as regards hearing harmony.
here are some ec players Iwould recomend for song accompaniment, all different, killen, turner, barber, clinging, kendrick, alf edwards,lea nicholson, pete wood. also listen to anglo players like Brian, and peter bellamy, much can be learned from listening to other systems of concertinas, even if it cant always be used.
here is a tip, For playing tunes like morris tunes reverse bellows more frequently, and avoid running notes into one another