For me the Sinner works fine in all positions with the mothers milk...I too was worried about the in-between tones but I do not hear a problem....Its not totally vintage correct however and maybe not the best route for achieving the ultimate in quack but the in between tones are still way better than stock...Again, I don't hear anything wrong, but it I have never bothered to do a direct comparison (probably will soon)...My wiring is conventional....Thats the only way to go with BK singles....vintage wiring all the way sounds best...
In between tones usually have a lot of dependence on the relative pickup heights. When dealing with damn good pickups anything is possible. A BK pickup, no matter what it's intended design is for, is versatile enough to do a lot of things...The sinner isn't just for metal, think of it as a versatile single coil.