HeatedNubbycake

Hi im new to the forums and modifying mustangs in general, and I had a quick question about installing a upr x pipe I just bought used. its a catted 99-03 x pipe and when I bought it it came with 2 pipe pieces (small and large) and the hardware to install it. now people are telling me It wont fit without a little 2 inch aluminum extension flare thing that goes on between the manifold and pipe. Iv seen conflicting arguments and I really don't know who to believe. any help?