Using CDN gets worse grades?

[VPCI]

Hello,

First want to say thanks for the site. Really helpful in so many ways.

Now to the reason for my post. I've been testing with CDN enabled and CDN disabled and I seem to generally get better grades here are webpagetest with CDN disabled. This seems counter intuitive to me. Is this accurate? Is there a reason why CDN would cause the grading of a website to go down?

Thanks.