Where, in Ireland, a six-footer's on edge (6)

I believe the answer is:

antrim

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'where in ireland' is the definition.
'antrim' can be an answer for 'ireland' (I've seen this before). I'm unsure of the 'where in' bit.

'a six-footer's on edge' is the wordplay.
'a six-footer' becomes 'ant' (ants have six feet).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'edge' becomes 'rim' (rim is a kind of edge).
'ant'+'rim'='ANTRIM'

Can you help me to learn more?

(Other definitions for antrim that I've seen before include "Ulster county" , "town in Ireland" , "Part of Ireland" , "NI town" , "Giant's Causeway county" .)

I've seen this clue in the Evening Standard.

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