I have been trying what you said. I have my default document on Inkscape set to 150mm by 150mm. I import an SVG and reduce size to something I can work with that fits inside the borders of my default document. I then save as a PDF. I use Convert2DXF to convert it. I use the BCLMode setting. But when I go to load it into BCL, I get errors/warnings, sometimes it's "Drawing Scale Warning".
I had an SVG that was 130x140mm and BCL says the "Drawing Height and/or Width is 1026.20344543457 MM" I have gotten the same Warning ( and the same 1026.20344543457 MM ) on several different files. I also sometime gets a warning that my object is in the negative space, -X or -Y and needs to be moved in my CAD program. I'm not using a CAD program, and my object in the SVG is within my 150x150mm document boundaries when I save as PDF.
Any insights on this? Is it Inkscape, Convert2DXF or BCL that is holding me back here? If any of you want, I can upload some sample images, in the original SVG, after I save as PDF, and the DXF output from Convert2DXF if you want to try to re-create it.