Good that you have observed some improvement Mark.
In line with what @PeeBee stated, checked my CRD fan blades_ would be lucky to covered 50% by the cowl skirt and radial tip clearance is nom 25mm (different eng mount and other flex characteristics but just reference info).
Guess U can only give a deeper cowl a go might even quiet it down a bit.
Mentioned it as in early 80's, I put a 4 cyl B series diesel in my FJ45 swb (two less cylinders than the original 2F petrol)_cowl extension made up using galvanized sheet/metal pop riveted in place, did not have a nutsert tool then.
So now, with the noise from the fan and the resonance from the CC cooler she must be buzzing with noise now mate.