Dry hopping is for aroma. Flavoring hops are done in the boil. I generally use lower AA% hops for flavor & aroma. But some high AA5 hops also have some interesting flavors,so some use those for flavor & aroma too. but pre-hopped extracts should NEVER be boiled. It destroys the designed in hop profile. If you want to do flavor hop additions,use some plain (un-hopped) extract in your partial boil. Add an ounce of hops at 20 minutes,then another at 10 minutes for some extra hop flavor. Then add the pre-hopped extract (Cooper's can) at flame out. Since it's still boiling hot,dissolve the late extract additions,cover the kettle & steep a few minutes. Pasteurization happens about 162F,& the wort is still 180+ at this point,so Bob's your uncle.