I have a Parlux 3500 too with a diffuser.

I find if I diffuse my hair with it from wet I get a bit of frizz but if I diffuse when about half dry I am left with nearly zero frizz.

I diffuse upright and hold the dryer above or level with my head.I do it that way 'coz I like to tone down the volume.
3A/B - m - ii - porous

Located in Sydney Australia