Exhaust question.

I was under my Jeep changing the oil today and while it was draining I was checking things out. I noticed that my exhaust changes size (gets larger) about 12 inches after the header/manifold coupler. Is this normal? It is a 1998 4.0 auto Government issued SE model. I had my friend take my Jeep out the other day and he says it has a lot more power than his 2000 does. Do you think this might be why?

Again I ask. Is this normal?

Here is a pic.

looks the same as my old one did. I put new header and cat bak so I replaced the downpipe aswell, but yeah my original one looked just like that.

Thanks