http://en.pruchabanjos.cz/uploads/how-to-setup-your-banjo.pdf

To place the bridge we add 2-3mm (5⁄64-1⁄8″) to that measurement(totaling 337-338mm)(1317⁄64″ –135⁄16″) to get the correct distance from the 12th fret to the bridge center so that it is actuallya little closer to the tailpiece.
The feet should always be parallel to the frets. In this position, you will have good tone all along thefingerboard.

Stelling’s Set-up System http://www.stellingbanjo.com/blog/stellings-set-up-system/

Be sure to brace the bridge with your fingers across all three feet if you have to move it forward or backward to the desired distance of 13 3/16″ from the 12th fret, measured from center of fret to center of bridge. Make sure the bridge is parallel to the frets and that the feet are flat on the head.