I'm nearing 12 weeks postop, but only about 8 weeks of dilation due to postop complications.
At first, I was having to use a Pratt Dilator - a small steel dilator with no taper and a slight curve at the end. That dilator would readily twist to follow the path of my vagina - right, then left, then up, and would even try to go down though I wouldn't let it go that way.
Finger examination revealed much the same as you described - the inside had numerous ridges - presumably areas where scarring had made the diameter smaller, or where tissue was naturally wrinkled.
I'm now using regular dilators, but, surprisingly, have been remiss in self-examination - It's time to go spelunking again. I have noticed that the path has straigtened completely - the dilator just goes straight in without twists and turns. I doubt that it will ever achieve the smooth walls of a natural vagina however - just thinking of the wrinkled tissue from which it was made.