Funnily enough I had a go at making my own image like that before seeing that one. I came up with this :
Shows the largest possible rounded boundaries by my google maps and paint skills at :
Red - MCG
Orange - Wellington
Yellow - Eden Park
Can't guarantee accuracy (westpac a slightly longer possible straight boundary than the MCG
?) but I think I've got the pitch the right way around in this one for them all compared to to the other.