Following are the methods by which you can control the length of the flange and can calculate the unbend length.

Inner	Enables to calculate unbend length of the flange from the inner face of the flange.
Outer	Enables to calculate unbend length of the flange from the outer face of the flange.
Exclude bend	Enables to calculate unbend length of the flange excluding the bend radius.
Bend line	Enables to calculate unbend length from the bend axis of the flange.
Inner tangent and Outer tangent	Enables to calculate unbend length of the flange from the inner tangent and outer tangent. The blue and red lines represent the inner tangent length and the outer tangent length of the flange, respectively