JanJ, as usual, you send me back to the textbooks! LOL! Wheeler & Clark in this case. And after poring over both species accounts, and going over Doug's photos, I'm still camping with Sharpie.
Except for relative size, the genders of both species are not sexually dimorphic. I can't tell from these photos the size of Doug's bird but am curious why you say this is a male...?
Undertail covert streaking on the juveniles of both species is thin. But the upper breast and belly in Coops have a consistently thinner streak, making them appear much more elongated than a Sharpie's streaking. Also, it makes a difference whether the bird is slightly fluffed (due to cold, e.g.) which can broaden the streaking's apparent thickness. But the shape of the individual feather's streaking is also different in each species. Cooper's again is very thin and has a more graduated roundness (almost teardrop shaped) where Sharpie's is wider and almost immediately bulbous as the streak descends. And in Cooper's, the streaking gradually narrows even more as it descends to the belly. In Sharpie, the more robust streaking stays robust almost 2/3 the way to the tail and then starts tapering off a bit.
I'm not sure the white terminal band is really diagnostic. Even in Wheeler & Clark, two different ventral shots of juvie Sharpies in flight show a wide AND a narrow terminal band.
Eye placement and head shape are difficult to see in Doug's photos due to angle. He says he has more tucked away -- maybe a good, flat side view would be helpful. :t:
Not that this gives any credence to my opinion, but in AZ where I lived for almost 5 years, we had Sharpies and Coops in the yard on a daily basis, a couple times even together (until the Sharpie spied the Coops and took off in a big hurry!). They nested on nearby properties and the birds that came to my bird feeders were the attractant to the juvenile and adult hawks. And even seeing them that much, I find photo IDing them still very, very difficult. In the field, not so much at all because you can look for and usually get the field marks.