Yes, I also tried to follow the tutorial guidance, and ran into similar scaling problems.
Then I looked at the source code for the VCV Free (nee Fundamental) modules, and discovered that VCV did not follow the recommended standard! The VCV svg files use pixels as the unit, with a height of 380 pixels, and a width of 15 pixels per hp. I adopted that practice, and everything has scaled perfectly. I am able to read the pixel coordinates directly from inkscape and use them when I add the widgets in code. Actually I read the upper left corner of my widget, as well as the width and height, so I can then compute the center point.
Within the svg, I typically get the width and height of the component svg and then create a geometric shape with those dimensions in my faceplate (using a layer that can be hidden). Again, I use pixels as my units. I have also had some success simply pasting the component svg into my faceplate svg (again on a dedicated layer). But pasting the actual svg can sometimes be finicky.
I have yet to have any problems with this approach.