It can depend on the shape of your diamond. For my cushion cut, I wanted a bezel halo. Since cushion shapes run the gamut, I wanted to work with a vendor that does custom cads for each setting, which is why I went with ERD.
If the vendor you are working with is already doing custom cads for you, you can mark it up so that they can see what exactly you want tweaked. If this is a modification of a standard setting they may charge you for the extra design/labor involved, unless the setting price includes customization.