This thread seems to be wrapping up, but I’m going to comment anyway. If you ever get a chance to take a flute workshop with Grey Larsen, by all means do it. I’ve taken several and come out a better player every time. He can identify how you can improve and teach you how to get there in a safe environment, which is high praise for any teacher.
I’ve also taken workshops with Kevin Crawford (2), Seamus Egan and June McCormack. While those workshops were fun and it was great to breathe the rarified air, I can’t say they made me a better player.
To answer the specific question posed: there is an orthodoxy that has developed in Irish flute playing; namely, all cuts on the south end of the flute are performed with the L3 finger and all cuts on the north end by the finger forming the sounding note. I find that the orthodox approach does not work for me in some instances, as on the second octave E and on a descending run from first octave F# to D, also cutting the E. I also have issues with flute stability when using the A to cut the A.
Which finger to cut with is only a small part of Grey’s book. I found his ideas on the percussive nature of flute playing particularly insightful. I also use his notation system when transcribing tunes.