In my previous life at Parafield airport we had the same issue as Moorabbin, constantly wider and wider circuits - particuarly when there is a tailwind on crosswind or downwind.
In a single engine aircraft - close enough to glide from a downwind position and comfortably glide in (0.75-1nm). Larger aircraft operate higher and faster, so flying the same sized circuit would not be practical. The aircraft I operate now (medium turboprop) we aim for approx 1.5-1.8nm spacing with a 1500' circuit.