The EST software currently only has the ability to set a single percentage for metal waste, and then it can be turned on/off as to whether it is applied to straight duct.
I suggest that a separate percentage be applied to straight duct as it would have a lower amount of waste, but there is still waste.
Autodesk has told me there is currently no workaround for this, and to list it here as a wish list item.
So vote for it if it matters to you.
Thanks.