It could also be a residual perception from the time of the Anglo-Irish Treaty to the subsequent establishment of the Boundary Commission that NI was probably only destined to be separated from the south temporarily.
Scotland existed as a kingdom in its own right before union in 1706 (/7?), whereas the Irish kingdom was artificially created out of the Lordship of Ireland by Henry VIII, around 1541 iirc, so it might be perceived by some in the establishment as a deeper union...?
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