Bias maps are RGB vertex color maps, with the vector being a color value. The values can be either in the range of -1 to 1, or remapped to 0 to 1 ( (value + 1) / 2, and use the remapped value check box)

The FiberFX tool in modeler makes Bias maps, though it's all manual. There were issues with my bias map maker in 2018, that despite having been reported and fixed, they still exist, and crash layout to the desktop when they occur. I think it has to do with LWO2 meshes being converted into LWO3 meshes, because that's where it occurs the most.

The style combing script does make the fibers flow around the object quite nicely - it's what 'sleekness' does; The higher the value, the closer it lies to the surface, similar to what the Sasquatch control of the same name does.