Tattie Bogle. thankyou for your post
I agree that the majority of bc players are not playing in c major, however i have come across older players in this area of ireland who were and who were using it like a c one row[ this is possible with the double ray model when the basses have not been retuned]
on the subject of differnces in fiddling it would be sensible to be aware of some of the differnces in regiional fiddle styles in ireland. Donegal styles have considerable scottish influence. and are differnt in approach to sliabh luchra style
northumbrian [english] music is influenced by northumbrian pipes and to some extent scottish musicand is imo differnt from southern english music.
will start to happen more as musicians gain more harmonic knowledge i think the use of harmony however i and my ex musical partner were using harmony back in 1980. here
https://www.youtube.com/watch?v=ItcBocS_x_M