On a large scale, the six Counties of Northern Ireland were deliberately chosen to provide a Protestant majority - three counties of Ulster were rejected because that would have put the balance in facour of the Catholics - classical gerrymandering.

Not at all.
The boundaries were deliberately chosen to include as many unionists as possible within the union, and to allow as many nationalists as possible to be outside the union.
It was an attempt to please most of the people most of the time, which is all you can hope to do in a plural society.