I suppose modeling programs can be misleading and only listening (testing?) is the real measure but 28Hz tuning on a 9ft3 box looked real bass shy compared to 40Hz when I modeled enclosures for my 604-8G (which I'm sure isn't the same as your 704).All I can say is that I'm very happy with a 40Hz tuned 9ft3 box for my G's. I don't know how much of a roll a wide baffle and dual side mounted vents of fairly large area (1 1/2" long) plays in the final product but I like the results.