If you crop the rounded edges out, without cropping the top & bottom, you’ll get around 2.20:1. I was talking about preserving the full height. It can be done. In the 2.39:1, you have cropped the top & bottom out, as visible from the lines.
Oh right. The issue with doing it that way is as Beber mentioned it introduces problems. That part of the frame is allowed to have abnormalities in it, and usually does. Anyway, the preview you see has been cropped but I don’t have the uncropped version.
And even if you did it that way, it won’t be anything like 70mm cropping as that’d done completely separately to a different master print than the 35mm. It’s probable that the 70mm version has more picture on all four sides.