That is not true. the Impul kit will fit for sure for the P11. There's no difference between the P11 here and the P11 over in Japan. The only difference is the rear suspension, the JDM P11 do not use the multilink suspension in the back as the USDM P11s that's why none of the JDM exhausts would fit our cars.
If you look at the dimensions for both the JDM P11 and our P11, you'll know that they are exactly the same.