I also found that the most comfortable position for me was near the center. My chin was always over the small ridge on the chinrest by the tailpiece. I changed both my regular violin and my electric to the center mount Berber model chinrest. Really like them. It allows you to hold near the center, but you can also move your chin to the left.
I'm not sure if they make them for viola, but check the photos of the ones for violin. It may be what you're looking for.
I've tried both the Wittner and Berber center chinrests (& others) on my violin. Of the center chinrests, I found the center mount Flesch (with hump) worked better for me—I liked the hump (or ridge) because it fits well under my jaw bone, & feels more secure. Very individual thing, though. A lot of people find this uncomfortable.
I played with center mount Flesch for a while, but now use a Wave (kind of in between side & center). I’ve talked about them here:
AndrewH mentions in one of these posts about the difference between violin & viola chinrests--that most only have different clamp barrel lengths.
@JohnG and others. No particular experience with that chin rest, but I have a great respect for Wittner. I have used their isny shoulder rest for years and they have been extremely helpful in providing me extra mounts whenever I requested one.
They generally use metric screws in their chin rest clamping system so adapting to a viola should be simple.
Without deviation from the norm, progress is not possible. —Frank Zappa
The future is already here—it’s just not very evenly distributed. —William Gibson