quote:As awkward as what?
As the English! "Bheith"/"being" in either one is extraneous for the meaning you're trying to convey.
It's not that you can't interpolate
bheith into this construction - you can - but then it's progressive (or "continuous"? leanúnach anyway) so the
níl...ach will tend to be interpreted differently.
Tá Seán tar éis ól: Seán has drunk.
Tá Seán tar éis a bheith ag ól: Seán has been drinking.
Níl Seán ach tar éis a bheith ag ól: Seán has only been drinking (but there's nothing else the matter with him.)
This topic is not overlooked in grammar books. Are you talking about grammar books, or self-study courses? I don't remember if the Christian Brothers' grammar in English discusses it or not but the one in Irish certainly does.