Read this first

Exhaust flow

Good example Rick K reminded me of

Some years ago Rusty Wallace in Nascar out of the blue began winning several racers. The exhaust sounded different.
Others did not know why until he crashed and car ended up lying on one side and everyone then saw the exhaust design.

The closer the X is to the heads the easier it is for it to draw the exhaust out of the heads leaving better makeup of air/fuel burn.

Further back the X is means there is more exhaust volume backed up to where the X is.

The center of X is open which allows the exhaust flow of one head to pull the flow of the exhaust in the other sides echaust pipe.