Taking a roll of 120 backing paper, I measured how far the actual film start is from the 6x9 '1' marking. 120mm. Considering that the 1 is actually inside the frame edge 10mm or more, this leaves a leader of 40mm or more with a camera like your Bessa. And explains why the Zeiss is such a pig with last frame spacing- there could easily be one, maybe 2, frames in the unused film area when you first load.
One of the issues with 6x4.5 (only) cameras that use the 6x9 frame track is that you have to leave a lot of leader to get the first 6x9 frame number to a ruby window in the relatively narrow camera. Realistically, these are 15-on-120; to avoid the short tail you'd start with 1 in the
second window. Newer 6x4.5 cameras, like my Daiichi Zenobia, use the 6x4.5 frame track and don't have this problem, but Zeiss cameras from as late as 1948 used the 6x9 track to start the auto-counter on a 6x6 or with two windows for a 6x4.5 only camera. which inevitably means you've got about half a 6x9 frame left blank at the start.
One way you could avoid "wasting" a frame would be to use film that has dots before the numbers (Kodak and .EDU Ultra do, for certain) and wind to the first dot instead of the number; on 6x4.5 that's about half a frame. You won't be able to tell at a glance what frame you're on, but you'll see the number as it goes by when you wind (before or after exposure, according to your method). As long as you do it
the same way every time you'll still get even frame spacing, you'll just be transferring blank film from the start of the roll to the end. I use this method for loading my 1948 532/16 Super Ikonta B, in which I've modified the stop wheel to allow 12 on a roll, instead of the 11 (started with the 6x9 track) the camera was designed for; I've actually found I need to use the second dot instead of the first or I get a short leader (on 6x6 -- first dot should be just about right on 6x4.8).