Sounds like a load of bollocks!
If you're visually circling in the circling area, it doesn't matter how you got there or from what angle. Obstacle clearance
in it is obstacle clearance. As for missed approaches, you'd always be doing those off the end of a straight segment, not operating inside the circling area, off the approach track, in IMC, surely? if you then do go IMC, well that's a different matter.
We use PANS OPS 4, and all our circling MDAs (and vis) are the same regardless of the approach used to get into the CA. Cat C: 4.2nm radius from the runway ends, 400ft above all obstacles anywhere in the CA.