Hi , I had this problem and have fixed it after I remember reading one persons idea.

The ramp end closest to the plunger has 2 bolts going through the playfield to secure the ramp in place. Undo the nuts and allow the 2 rails to be higher on the top of the playfield. You may need to push the ramp up from the bottom of the playfield. ( This effectively allows the ramp to start earlier so the ball rides the rails earlier.)
Such a simple fix but why I didn't do it earlier and persisted with the shooter plunger , the wire switch etc etc I'll never know. It gets up the ramp everytime now.

Now I have to sort out why the F9 fuse blows after multiball - something to do with the magnets I expect. Help please.