It's just a consequence of where the ball is placed, and it cannot be avoided. Well, it's possible to make a gentle ramp to diminish the presence of the ball when closing the knife, but this happens over time with normal wear and tear for the ball and/or tang (the ball carving a circular groove in the tang vs. the tang grinding the ball flat).
No one ever takes that approach for good reason; you do not want to encourage wear to the surfaces involved for a lock. The ball is a protrusion that must be overcome when you close the blade. When doing so, it creates an air gap so that the lock bar does not scrape against the mating surfaces in the tang which would lead to a loose, inconsistent lockup over time. The ball is also there to allow smooth folding action. Less area to scrape, since it's a ball and only contacts the blade at one, small point.
I did searches for "ball detent wear" and found these threads:
http://www.spyderco.com/forums/showthread.php?54976-Ball-detent-carving-a-groove-in-blade
http://www.bladeforums.com/forums/showthread.php/968893-Detent-wear-on-liner-lock
(See post #5 for an interesting approach to reduce wear)
Story time:
The first knife I had ever taken apart was a bootleg Subcom (my gateway into knives was then an authentic Boker Wharcom).
I figured out how it worked. I noticed the same behavior you observed. I took a Dremel to it and forced a groove in the tang where the ball would create a track by normal wear and tear, but then noticed the lock bar contacting the tang. It didn't feel the same to use. Less snappy, more loose. Where I really messed up was actually grinding away at the lock bar itself to make it engage more deeply. It developed play and was difficult to close (probably because I left it rough). A nice $3 spent to learn about frame locks first hand.
Some of us own many folders because we just love to play with them—open and close them, without actually needing to cut something. Prolong the life of them, distributing the wear and tear by having several
