March is the first month of the long season. The Southern Ocean lows start tracking close enough to send south-west groundswell onto the Eastern Cape, and the published figures put the coast in the three to six foot range from now until October.
What matters at J-Bay is not only that the swell is bigger but that it is longer. The point is a chain of sections, and it takes period rather than height to link them into the ride it is famous for. March gets the first swells with that in them, which is why the month reads better than a summer month of the same size. The water is at 20°C and a 3/2 goes back on.

