I think the only "technique" issue would be if you are actually inserting it to 18mm at the stricture. The other thing might be frequency. If you are dilating daily I think that is the best it will be.
What we don't know is if your stool is too thick, if you have pelvic floor dysfunction, or pouch prolapse/twisting. Anal dolation would not affect these things, just anal stricture.
Jan