Vince,
You should never use the fence and miter slide at the same time...for this cut, it's much more important to use the miter (to keep the workpiece perpendicular and straight).
This kind of cut never feels "natural" on the table saw (with the board sticking straight up), but if you set things up properly (I'd use a substantial piece of wood as support), there is no need for the fence...just take multiple passes, moving the piece over a bit at a time.
You run the risk of binding things up (and perhaps tossing wood/fingers around the room)....be safe with your table saw...don't use the miter and the fence at the same time!
deknow