A little background, for those *really* interested..
Originally, one of the first lock designs had no ramp there and no flap up at the far end (entrance) of the lock. The exit of the lock area was angled down-playfield. (If you look at the kickout, you'll see the red lane artwork on the playfield is still angled down like this.)
The problem with this was that balls shot into the lock would shoot around that tight corner at the entrance, and go flying into the lock. Ball speed would be to fast that the ball would then jump out of the kickout into the spiral. The lock exit was changed, to straighten it off, to stop ball bounce-outs. This didn't really work well. So, the alternative was to slow the ball down - by sending it up a short ramp to then get deflected back onto the playfield, taking a lot of momentum out of the ball, so it wouldn't go flying out the bottom of the lock.
The problem with THAT was that space was so limited, that on a hard-enough shot, the downward deflector would cause the ball to hit the end of the ramp, lose ALL momentum, and come rolling out the entrance.
In that thread, I mentioned that I used lock-nuts to raise up the back of my lock cage, because my plastic spacers were pretty much squeezed completely out of shape. After over six months of playing, it's still not 100% - I actually have balls coming out of the lock exit now. My deflector isn't angled right to slow balls down enough sometimes. (Maybe, 1 in 10 shots when lock is empty.) So it's a tweak I need to get to.