Does "small of back" mean "over spine"?
I've always considered it to mean fully behind the hip - lets say 4:30-7:30. You can wear your gun pretty far back without actually placing it over your spine. The upside to holsters marketed for SOB carry is that they're canted further forward to allow a smoother draw.
You can also get a holster with adjustable cant and see where works best.
si vis pacem para bellum