BOAC,
It might have to do with
"5.4.4 OCA/H for visual manoeuvring (circling)
The OCA/H for visual manoeuvring (circling) shall provide the minimum obstacle clearance (MOC) over the highest obstacle in the visual manoeuvring (circling) area as specified in Table I-4-7-3 of Chapter 7. It shall also be:
a) above the lower limits (also specified in Table I-4-7-3); and
b) not less than the OCA/H calculated for the instrument approach procedure which leads to the circling manoeuvre. See Chapter 7, “ Visual manoeuvring (circling) area”."
With the different approaches they have different "OCA/H calculated for the instrument approach procedure which leads to the circling manoeuvre" because of the different splays due to the accuracy of each approach design final segments.