Following up, I've tried the following - it seems to work exactly the same in all cases.
- 6.3 download, stock
- 6.3 modified as shown above
- Ubuntu distribution version
- 'Portable' all architecture version
I also tried to get the Java Web Start version working with suggested parameter mod (" -Dcom.eteks.sweethome3d.resolutionScale=2") I don't recall if I got that working, but if I did it was just the same.