Bevel Width selects how much (0% to 100%) of the frame is beveled.
Note that Bevel Width actually selects the percentage of the frame
that is not beveled so it may appear that it works in reverse
to what you expect. So at 0% all of the frame is beveled and at
100% none of the frame is beveled.
The following example shows Bevel Width at two different settings.
Bevel Width = 40
Bevel Width = 70
Also note that this control was named Frame Width in versions
1.0 through 1.2 of Picture Frame and at that time Frame Width was
named Width. This was the result of an attempt to be compatible with
a naming convention that evolved with the BorderMania filter set. But
it caused too much confusion in Picture Frame so Width was renamed
to Frame Width, and the original Frame Width was renamed to Bevel
Width.