Face instancing and scale, non-proportional (DupliFaces)

I want to utilize face instancing in a current archviz project for all the windows, too. The modeled window is separated from the main house window cuts within the walls. So far, so easy. Since a lot of the cutouts for the windows have different sizes for width and height, the main window instance should scale according to my face sice. If you enable the scaling option, it only allow for proportional scaling, but this is not what you want for windows, since they stick with their thickness and just adapt to width and height.

I had 2 readings in the Blender docs for this part, but i dont think the scaling is treated properly.

  • The initial scale from the object to the instancer seems off, even if they share the same bounding box dimensions and vertex positions. If you adjust the scale factor to .5 it seems somewhat close but still scales off the original boundarys (is the scale factor a midpoint value like for displacement?)

So do i hit the limitations here and have to use destructive and performance treating shift+d for every window?