It isn't offset, just down the middle. I've experimented with bolt on and welded mounts of the same design. The advantage of the bolt on is that it can be moved to another bike...of the same frame measurements, obviously.
We've high jacked this thread but maybe it will serve a purpose of education, if not just displaying what different minds can do to solve a problem.
By the way, that bushing is a very stout item. No resliency you can discern. It's hard as a rock
Have a good ride.