Hi Mike,
The Grizzly website includes pdf manuals for their sheet metal brakes,
including the pan and box brakes. Take a look at their G0578 40"
model.
In the drawing on page 16, the forward edge (point) of the fingers is
vertically above the edge of the base, so no clearance has to be
allowed here - it's all taken care of by making the bending leaf
adjustable.
The G0578 manual on page 16 states that this "setback distance is
adjusted to at least 1.5 to 2 times the thickness of the workpiece, and
thicker or tempered workpieces will need a larger setback."
Hope this helps,
Ian