The slug isn't pushed completely into the liner, only enough so that it sticks without movement. A slight push with the thumb is all it takes to do that. Since it's conical, it self-centers.
Once it's 'stuck' in the muzzle, then it becomes your marker for clocking, instead of trying to mark your liner end and erasing it with removing/reassembling the liner tensioner.
1.) Remove the tensioner from the liner/shroud.
2.) Mark the 'clock' positions on the side of the liner that is sticking out from the shroud (most go at least 4 clock turns: 12-3-6-9 o'clock for instance).
3.) Insert slug with the etched mark into the liner, NOT all the way in, just enough so that it doesn't move, and is in alignment with say 12 o'clock. It should be sticking out past the liner muzzle a tad.
4.) Reinsert the tensioner watching that the mark on the slug moves to the correct location (Top Dead Center).
5.)
NOW, remove slug with tweezer (BE CERTAIN TO REMOVE SLUG BEFORE FIRING!!).
6.)
CHECK TO ASSURE THAT THE SLUG HAS BEEN REMOVED!! Test fire to verify POI.
7.) Repeat until all four 'clock' positions have been test fired by moving the liner to Top Dead Center (12 o'clock to 3 o'clock, then to 6 o'clock, then to 9 o'clock) and aligning the slug mark to each new clock setting after moving to Top Dead Center.
8.) After getting the 'clocking' complete, decide which one is correct (normally the one that prints closest to Top Dead Center), then remove the marks on the side of the liner that don't work and leave the one mark that does (say it's 3 o'clock, so remove 12-6-9 o'clock marks).
From then on, after the need to remove your liner for any reason, always use that mark (the one 3 o'clock mark) to align with the slug mark and then tighten the tensioner to align to the Top Dead Center position
(AGAIN, REMOVING SLUG BEFORE FIRING!!).
It's a little tough to explain, so if you still have questions, just ask or PM to clarify.
mike