I like the new sti tubes with grams spring and followers with a 4mm taran tactical base pad. Mike the feed lips they should be about .380". The tubes out of the box with this combination runs great for me. I get a reloadable 21.
I have a back up for both my limited and open pistols. Last year at nationals I had to use parts from both my limited pistols to get one that would run. Both minor problems. I will not shoot a major match without a backup.
Have you adjusted the lips on your mag. Sounds like they are to wide allowing the follower to come up to far. If it is .40 a cal I think they should be around .390 or so. Call Bobby at Freedom Gunworks to get the exact measurement.
I have always wondered about this myself. I shoot my limited like my open in that I put the front sight on what I want to hit. From the discuss I gather that is what you mean. If not could you go into more detail?
I use the same setup as you do and only get 20 in the tubes that are not tuned. I have two that Bobby at Freedom Gunworks tuned. With bolen spring and follower and a bolen 4 mm base pad they are a start able 21.