I am not sure that setting the bullets back by using a bench or your thumb is what anyone is after. Just load your bullets fire your gun once and then take your callipers and measure the remaining bullets and see if you have any set back. If you do have some set back (C.O.L. less than when you first started) then crimp a little more. I run my taper crimp die down to the case then give it a 1/4 turn more and it seem to work fine. If you want to measure the diameter of the the case mouth after crimping then put your callipers on the case mouth and measure there. I believe mine measures around .377,.376, my cases have not been trimmed to the same length so my crimp varies.
The only reason that I crimp is that a while back I was haveing a little trouble getting my bullets to feed so I started to crimp and the feed problem went away. Ok, the real reason is that I loaded for 9mm and S&W 40 and had no real problems until one day I started to load for a 38 special and it took me 3 weeks to figure out that I had to crimp my rounds to take out the case bell in order for the bullet to fit into the cylinder of my revolver. (Guys on this forum helped my figure it out) After that I started taper crimping everything. Now let just say here that the 38 special rounds I load (So far) are not cannelure d and that the 38 special round is something completely different than what we are talking about here.
Mostly if you don't bell the case mouth more than what is necessary then you should not need to taper crimp your loads. I never had a problem with set back in my 9mm, S&W 40 before I started to crimp. So the best thing I can tell you is to not over crimp and use a taper crimp on the 9mm but I cannot tell you how much is to much. As a rule of thumb when first starting out in reloading just puck up a factory round and start from there. Just measure a store bought round and see what the measurement is at the mouth of the case and start there.