Voigtlander Bergheil: What lens?

I'm curious how the changeable lens feature was originally meant to work (I've got a 9x12 Bergheil with the standard 150/4.5 Heliar). The Bergheil body has a metering scale but presumably that would only work for lenses of a specific focal length. If I put an original Bergheil-mounted Tele-Dynar 290 (255?) mm onto this body that came with the 150mm Heliar, the Dynar will have to be 290 (255?) mm away from the focusing surface in order to focus. Meanwhile the metering scale was presumably for a 150mm lens - which would have to be 150mm from the glass/film. So the metering scale with a Dynar on will completely of the mark. Likewise if I were to manufacture the Bergheil bayonet and put it onto say a 135mm Tessar, the metering scale would be completely useless again. The whole Bergheil original 'changeable lens' concept presumed focusing on the ground glass only, except with lenses of some specific 'standard' length, is that correct?

My Bergheil came with a 135 lens from an Ica and had a homemade focus scale added, but yes, non standard lenses would require ground glass focus. It was owned by a female news photographer btw.