No, I haven't done that much testing as it can be the sensor placement, the focus screen or the mirror. And of course "operator error" which it is not.
I have an R9 with Brightscreen focusing screen, and right now the DMR sits on a R8 with ordinary R8 focusing screen which has a bit less backfocus; not the screen but the whole setup, either it is the sensor placement, the focusing screen or the mirror.
It's so small adjustments it has to be done by Leica or some technician. You go nuts trying to figure it out yourself. And as for focusing screens, there could be small tolerances between different brands, though I think my Brightscreen is a Leica screen modified.
I have had the same focusing problems on my two Leicaflex SL which, in turn, has been off focus. Again, this could be mainly the mirror as the focusing screen sits tight in those. Or the whole body out of adjustment from bumps, etc. But what I did then was just changed camera and after a while the one sitting might have changed back in focus! Anyway, that is a historic problem now, more or less, could also have been the film plane - and in some instances, simply the user.
The good thing about the digital age and the DMR is that you can test and know rather instantly what the result is of your tests. So for sure the problem is in the camera why it is simply a matter of getting the whole camera adjusted.