I'm not able to wear appendix style, so I don't have that exact model. I wear the IWB 3 about 4 o'clock. I'm right handed. Mine has the 1.5" clip and full guard. The clip is very secure with my belt from Midwest Leather Works (an NFOA sponsor here in Omaha).
The "extra tuck" option is for the AIWB. It's one of their ways of trying to "tilt" the gun for better concealment. It's an alternative to the "wedge". They show a comparison of those two options in the FAQ.
http://www.jmcustomkydex.com/FAQS.htmlFor some history on the wedge: A guy in Oklahoma by the name of Spencer Keepers designed a "wedge" for his AIWB holsters (
http://keepersconcealment.com) which "tilts" the gun in a way that it presses against your body. You can see it in this video starting at 0:31 attached to the body facing lower portion of the holster.
Personally, I'd probably use a wedge over the super tuck option. The downside to the wedge as folks have learned is they compress over time and eventually need to be replaced.