Gonzo, you are still talking about the sensitive area, not the critical area.
The localiser critical area is equipment specific, but is nominally 300m in length and 120m in width.
The localiser sensitive area is dependent on the ILS category (I/II/III) the number of elements in the localiser antenna and the obstruction within the sensitive area. For a B747 in the sensitive area of a 14 element antenna on a Cat III system, the sensitive area stretches 2750m from the centre of the localiser antenna.
These figures are from ICAO Annex 10 vol 1.