One of my greatest issues with Nemesis is exactly this point. Scimitar is pretty large, and can't maneuver past a certain, albeit respectable, envelope. Once "hit", though, it should have been relatively easy to project course and keep hitting it - each additional hit provides new course information. And setting torpedoes on more of a "proximity" setting (e.g. blow up when you get -here-) would at least guarantee some damage.
Oh well, its all in the writing, we needed a cool crash scene.
You're forgetting the role of evasive action on the part of the Scimitar. Even cloaked, the helmsman would be making evasives to prevent exactly the scenario you propose...