We don't really know that information Coops. As it stands it's only a theory that the size discrepancy is being caused by nearshore bathymetry. Yet, as it's a regular, well-observed occurrence it seems it has to be due to the ocean floor (and not, say, the swell-producing properties of any one storm).
The most obvious example is longer period (10 sec+) south swells and how they hit certain regions much harder than others. Shellharbour seems to cop it, while Wollongong and the Coal Coast don't get as much. Cronulla goes off, while the Northern Beaches goes without. Newcastle also reacts well to those swells.
Each of those regions has a north-south running coastline and, at least on paper, they should all get as much swell as each other.
It's been a theory brewing and it came to the boil during the Big Saturday swell that saw Vooey and Barrack off tap. That swell had periods of approx. 14 seconds so the effect was amplified again. Voodoo and a few other Bate Bay reefs were 15 foot while the largest wave on the Northern Beaches was probably 8-10 foot at Long Reef. Makaha was 8 foot. Newport Reef was a thick six. RP's smaller again and Queenscliff Bombie didn't break. It just didn't make sense...
Hence the only viable explanation at this point (and remembering it's been something we've observed for a while) is that it's due to bathymetry: certain areas have bottom contours that are conducive to attracting and steering longer period swells to the coast. The long period wave energy is travelling deeper in the water so it feels the floor earlier.
The answer to your question is that we don't know what the optimum period or perfect direction is, however it's something to be aware of the next time a similar swell shows on the map. Of course it would make sense that swells from every direction are susceptible yet we don't get enough north or east swells to really observe what locations operate best and how they compare.
Waves Misbehavin' article
here