Alright gents, my IMDN LE auto-launch out of the box was working correctly about 2/3 - 3/4 of the time.
I checked the ball guide and it was nice and straight and set to the furthest out/highest setting without bending anything. When the ball shoots successfully it seems perfectly aligned. However, some of the time it will either hit the black rubber post below the left loop entrance, or the tip of the small flipper across from it (so too low or too high).
So I tried messing with the autolaunch coil power settings a bit, no appreciable difference in the success/failure rate, but it does give a bit of a choice of whether when it fails you want the ball to have enough force to possibly give you a super-jackpot sometime, or just roll part-way up the ramp and then dribble down the middle.
I also took a look at the auto-launcher itself and I believe that it is the source of the problem. It is simply not built to the kind of tolerances that will keep the prongs centered reliably on the ball. It is very sloppy, and the single lightweight metal arm on the right side that is triggered by the coil firing naturally causes a sideways twisting pressure on it that can cause the prongs to be slightly higher on one side than the other, or even make both prongs move to the left away from center.
I even tried to introduce more tension in the shooter prong piece by bending the two arms below the playfield further apart so that there would some tension when it was tightened and it would be less sloppy side-to-side. This was effective in reducing the side-to-side sloppyness when using light pressure but not enough to hold when the coil fires. Even the bushings used around the rod that holds it are too large with enough of a gap to prevent it from staying perfectly straight. The net result was 0% improvement, still works 2/3 - 3/4 of the time.
So I don't think this can be solved without someone creating a replacement launcher, or maybe an upgrade kit for the existing one. Stern's launcher is as cheap as you could possibly make it, I think the metal on it might actually float it's so lightweight...
First handyman to craft a reliable autolauncher get's my $100.