I don't know anything about sizes. You could probably do some googling for information on the sizes that people have flushed out.
If you want to do a flush. I recommend drinking fresh apple juice for a week (I mean, get a juicer and lbs and lbs of green apples), which is said to soften the stones. Then do a flush.
I only know that my stones were listed as "small" in my radiology report.
Weigh your options. If you don't do it, you get your gallbladder out. If you do flush and are prepared to have surgery anyway, then either you get the stones out or you end up in surgery.
I'm not sure what I would do in your situation. I can't stand the surgeon I talked to when I was in the ER. If I had to do surgery, I would go to the next town over to do it. I know the guy I talked to would just laugh his butt off if I suggested a flush.
I wish I knew what to tell you.