This should be a FAQ, for sure.
There's no exact right spot -- by design, the liner changes position with use.
When new, I like to see at the very least the entire liner engaging the back of the blade tang. I like it a bit left of center, so it has plenty of room to wear. If the liner is too far left (partially hanging off the blade), snapping it open or lightly rapping the spine will usually wear it in quick, moving it so it engages to the right more.
I have not noticed that the place where the liner engages the blade is correlated with liner lock failures, provided the entire liner engages the blade. There are plenty of knives that have the liner way to the left, and the locks are very solid. There are plenty of knives whose locks are in the center or to the right, that have auto-disengagement failures.
One nice thing about the liner lock is that it's a self-adjusting mechanism. As the liner lock wears, the liner gets slightly shorter. If you'll notice, the blade tang is cut at a slight angle. That way, as the liner wears and gets shorter, the liner simply moves over to the right slightly, where the tang is angled back further. This keeps the lock free of play through the life of the liner.
When the liner moves all the way to the right, the lock is nearing the end of its life. Once it's all the way right, if it wears just a little more, it will introduce play in the lock-up. Or even worse, on some knives, it will jam between the liner and the blade.
At this point, you can go buy a new knife. Or, if the maker or manufacturer offers this service, you can replace the liner with a new one, or replace the stop-pin sleeve with a slightly larger one. A larger stop-pin sleeve will move the liner to the left again.
Joe
jat@cup.hp.com
[This message has been edited by Joe Talmadge (edited 04 February 1999).]