Bend Deduction of Hems and fudging the K-factor

I am curious as to how people are using the Bend deduciton etc properties for Hems. I am having problems getting good flats that match my hand calculated flat dimensions.

Any advice. I seem to only have success when I fudge my K-factor until the flat matches my hand calculated value, of which I use no deduction values for the hem flat.

See attached pdf for image of the type of hem i am talking about in this particular example

Joe

SolidworksSheet Metal