I remembered this thread from a week or so ago, as I've just got a Metz 45 for use with my TLR to replace a smaller national flash (mounted on the side bracket).
That National produced stong lateral shadows - not dreadfull, but intrusive enough to want something better. Having now run a couple of films with the metz, and comparing the negs I can now answer a couple of your questions.
The Metz 45 still produces shadows, but the added height helps a lot. With the small side mounted flash, there's a dark halo to the right of each object. It's made more obvious as its laterally matched to the shape of the object. By moving the light source up (with the metz 45) the shadow is moved down, so it doesn't quite line up, and is a lot less intrusive.
For optimal results I think you'd want the flash close in horizontally (minimizing the horizontoal shadow), and high (maximizing the down ward shift where its less obvious). Of course if you're shooting colour you want the flash sufficiently far away to aviod red eye.
This is from the results on a couple of films I shot at the weekend, so its not conclusive, but the metz 45's handle mount design definalt helped.