I keep going back to your Coopers and Sharp shinned hawk pics, I thought I was shooting at a Coopers hawk in my street, but now I'm not so sure? does the Coopers always have the white at the tail?
These two are tricky.
Yes they are thers a lot of overlap.
I find the robustness ,which Kevin mentioned, to be
my 'go to' distinguishing factor when
I see the bird in person. Coopers usually has more white at the tail tip but edges wear and that may not be what you see, same goes for tail roundness, if seen from behind and the bird is molting its retrices , then it may appear squared on either, if the bird is in flight with tail fully spread, the squareness isnt entirely reliable , the overall size of the species comes very close to overlap, and is dubious to eyeball. So .. -The gray nape of cooper adults is a securest call, if the black of the cap goes below the eye is a good ID for sharpie, if they are gliding , the position of the wrists relative to the head ( more bent on the sharpie) is also reliable , if the flanks with wings open are spotted with blotchy squares , go with sharpie, if the bird is perched and you can see the undertail , then the stacked ends of the retrices should line up on the sharpie , and clearly not line up on the coopers. if the tail end has heavy white edge , go with coopers. consider what you have for any given view in total and make the educated assertion.
But for me, like I said , in person , the impression of basic heaviness of the bird is quick, dirty and usually correct, esp. regarding the
square heavy head and thicker feet ,on the coopers. .
opinions will vary