Roger wrote:
as I recall you need to maintain MDA until within 30 degrees of the runway.

There is no such requirement. The AIM (5-4-19-f) just says:

Pilots should remain at or above the circling altitude until the aircraft is
continuously in a position from which a descent to a landing on the intended
runway can be made at a normal rate of descent using normal maneuvers.

On an approach like http://204.108.4.16/d-tpp/0507/09390G4.PDF (Ellenville,
NY GPS-4, CTL), the MDA is almost 2000 AGL. No way in heck you'd be able
to land if you waited until you were almost established on final before
going below MDA.