IP3 with bandlimited Guassian noise

I'm trying to simulate the IP3 with matlab. I find if I use 2 CW tones as Jammer, the iIM3=3*Pji-2*iIP3. However, when I replaced the CW tone with bandlimited Gaussain noise, which means the Jammer has the bandwidth like 1MHz. The IM3 reuslt that I simulated had higher power than the formula iIM3=3*Pji-2*iIP3.

Why the IM3 increase?

Thanks

Spectrum Regrowth.