apparent sheeting angles for self-tending stays'ls

[osteoderm]

I have conventional inboard side-deck tracks for my (non-selftending) staysail, but am looking into ways to make the small working staysail self-tending. The trick is, I'd like to keep my large flush foredeck free of booms, lines, and other contraptions.
I'm not sure what the rig is called (too modern), but I like the look of the self-tending rigs where the sheet is led vertically down from aloft to a track or horse, and then to the stays'l clew, with or without purchase.
Because I'm cheap/poor, the usual curved track and roller car just isn't going to happen... but a burly old-school bronze rod horse is totally do-able.
The question: For such an arrangement, what is the ideal width of the track/horse? Is there an ideal width? Would I best shape the horse to the sail, or build the horse to make a 10-12 degree sheeting angle (approx), and let the sailmaker build to suit?
Any ideas?