Exhaust piping question

I have got my new catback and headers. I have the 2003 l4 tib. The headers are obx and the cat back has full 2.5 inch piping. The header didn't come with an aftermarket down pipe, so I'm stuck using the stock down pipe where there is about a foot of 2.25 inch piping and then an oem cat. Will this small amount of small piping defeat the purpose of the whole system? Would I be better off to weld larger piping into that spot? I'm just curious if this small piping will negatively affect the sound/performance gains.

Thanks I'm advance!