If the ult works well with 1 shim then its fine to use that way. Increasing the number of shims reduces the distance the sear needs to move after the on-off closes before it can release the bolt. Thats all.
The leak in your powertube has nothing to do with the powertube tip. The leak is due to the carrier oring. If you have shims installed remove them. That alone might make the leak go away. The oring might not be bad. It may just be broken in causing a loose fit. Use the same white carrier oring and install the next tighter carrier size.
Except for the Automag in front, its usually the man behind the equipment that counts.