I can get by with a minimum of 30 degrees or so to the lean, it will then miss the fence. So which is best. I'm not sure cutting at 90 degrees to lean will be safest. At 90 degrees to lean, won't there be a tendency for the hinge to start ripping out on the tension side and then the tree goes where I had not planned for?
90° to the lean is physically possible. Given further modifications to the face, a tree can be swung even more so. HOWEVER, if you've never swung trees, this does not look like a good place to try your first.
That said, if you're feeling saucy and accept the risks, a 30° does give you more margin for error. I think I read in one of your posts (forgive me if it was someone else) that you had "The Fundamentals of General Tree Work" on order; if memory serves, there's a chapter dedicated to helping pull trees with a rigged line (which you said you were planning). At 30°, you might be able to get away with a full width hinge that is fatter on the tension side. *Might* because as always, it's hard to fully judge a situation without being there.