Does the part come into SheetCAM at the same scale as the AD drawing?
Meaning if the AD drawing is 1/4 scale, does the part come into SC at 1/4 it's true size?
If so, maybe you need to create a drawing format that is actually larger than your part so you end up with a drawing scale of 1:1, create your AD drawing from the model on that sheet format, then export as DXF. Maybe it will retain scale. Just a thought....