DXF has no concept of scale, and you have to select a scale when you export DXFs. The laser software (EasyCut) assumes a millimetre scale. In other words, a DXF will contain a unit-less dimension of 1.0; and that could be 1 inch, 1 metre, 1 foot, or 1 millimetre for all the DXF format and/or reading software knows. No scale issues have been seen when using MM for export from various CAD packages.
Box Generator generates arbitrary finger jointed boxes in SVG format. Use Corel to convert the SVG to DXF.