Maybe learning something new and that could be a good thing.
Let me preface by explaining that I purchased a Rollimat last year to try to do the very best job I could on a rebuild / restoration of any clock that comes across my bench, BTW I really like this tool.
So with the pivot polished and straight I then go to the bushing, selected for height and diameter ( most of the time KWM to keep the o.d. smaller).
Once the bushing is installed I fit each arbor to the pivot with a tapered reamer. Both from the from and the back of the plate shooting for the same distance on the reamer on each side. If you could see inside the bushing you will see a slight taper from the outside of the plate to the center of the bushing on both front and back. I then follow up with a tapered smoothing broach again from each site of the plate.
Reamers are tapered I am guessing for that purpose? I was told by a very good clock guy that this will reduce the amount of friction verses a straight bore? Was he wrong? I finish up the bushing by cutting or dressing the bushing with a circular cutter to create an oil sink. This also reduces the i.d. length slightly, keeps the arbor proud of the bushing.
Please comment if I am off base.
I do pretty much what you do but like Willie said, this is where the theoretical and the practical/possible come head-to-head. Ideally, the full length of the pivot should be supported but unless you have ultra-precision tooling to set the bushing and true-bore it, it isn't going to initially contact the full length of the pivot, and if there is any misalignment or flexing of the plates (common in mass-produced clocks) the pivot will be pinched. If the bushing is slightly tapered from both ends to the middle, it will be more tolerant of any slight misalignment of the plates. I maintain that either way (double tapered or straight) the pivot will initially be in contact with only a small part of the bushing - inside opening, outside opening, or center. After some time, the pivot and bushing should wear in and become in full contact either way. Obviously the straighter the bushing and the smaller taper, if any, the shorter the wear in period and the less debris that will accumulate during the process.
I have not seen this mentioned, but ideally, I think it would be desirable to disassemble the movement after the first year and just clean all the pivot holes and pivots with no broaching or additional machining unless a problem is found. Of course no one is going to want to pay to have that done so we just give it our best shot.