Fiddles stage right is certainly traditional in ensembles. Possibly something to do with the way right hand people hold their instruments, and where the sound is directed? I can't quite figure out if there is any logic in that theory.

It is traditional, but thinking about it now it would make more sense for fiddles to be stage left; my thinking being that they naturally turn to their right in the standard playing position, so would be facing more into the centre of the stage/auditorium if they were stage left.

Similarly it would make sense for the talented and creative geniuses in the flute section (no bias or personal interest there!) to be stage right because the barrels of the flute are therefore pointing out the edge of the stage and the musicians facing slightly inwards in their natural playing position. Unless Michael McGoldrick has joined in of course.

Maybe the traditional arrangement is so that both the fiddlers on stage right and the flautists on stage left are kept more comfortable by all facing slightly away from the accordionists in the centre :)