Fructose Mild Absorption

In the small intestine and in the large intestine that you see increases in methane and hydrogen. If it's secondary to SIBO, you generally see it in the small intestine, but not in the large intestines. So why does that necessarily, I don't understand how you know that from a breath test necessarily? Why does it necessarily have to be the case that the bacteria making the gas show up in a different pattern like that when the problem is the genetic lack of the right.?