Expansion chamber follow highly complex designs, especially mx style, and are not to be taken likely. It'll be that way for a reason. Either they've spent lots of time developing the shape for optimium performance. Or that this was the easiest way to get okay power and for it to be mounted. They would be my ideas at a guess. I never rated Athena. After shelling out £££ for their big bore kits only to be extremely disappointed. But be interesting to see what the Big bore and the pipe together makes.
Personally, I struggle to see why any unbranded company could go to the lengths that the bigger companies go to like DEP to ensure that you get optimium power output and shape. I've heard it alot with the BigOne expansions that they just don't cut the mustard.
Personally the best way to get power out of a two stroke exhaust is underslung.
Just look at the shape of a big'un compared to any other xpanny for the DT on the market, the shape of them is terribad. (my basis for stating it as a fact is based on a lot of other people's opinions that share mine ;p)
It's like seeing a morbidly obese girl walking down the street wearing skin tight leggings around her mahogany tree trunks.
In their head they think they look hot as fook, but in reality it just doesn't go!