Most circuits as taught by instructors seem to end up with the aircraft established on finals at 400'. Beginning a turn at 500-600' would therefore seems a sensible height to begin the turn onto finals at.
With the exception of circuits that are widended for noise abatement, we will be flying circuits exactly the same shape (in plan) as your own, and as you say, we just start descending earlier to end up as the same place for finals.