Because you have a stepped wall there are in essence two areas to light. Careful positioning of a single light could do the job resonably well. I think that two smaller fixtures on separate dimmable switches would give more comprehensive coverage. Remember that a 20" foyer light will likely be at least 40" tall and will have quite a presence in most entries.

Thanks for your comments roadbike. I think we are either going to install two smaller fixtures (separate dimmable - what a GREAT suggestion!) or a track lighting fixture. We were at a lighting store in the city last weekend and the sales manager suggested going with something like that. DH became enamored with the idea. I am hesitantly mulling it over. I know it will light the area well, I'm just not sure I am ready to commit to a look that is so contemporary right at the front door.