This is exactly what I am saying. If the h pipe adds volume and it picks up HP, you either need a bigger primary tube, a bigger or longer collector, or a combination of any or all of those things.
Those x and h pipes are a band aid in most cases. Unless of course, you are trying to run down joe Gibbs for the money.
Funny thing is, I never see Comp guys or even most fast bracket cars don't use them. Unless they are required to use a full exhaust. Then maybe, because of rules, it would help.
As I pointed out, if the SYSTEM is correct, most likely you won't find a gain, and will probably find a loss.