Remove the glass. Lift playfield up and lean back. Put the lockdown bar on and look in there with a light. See the bar that goes back and forth and into the notches on the lockdown bar legs - is that bar moving up and down okay with the brass screw adjustments or is it only able to go back and forth ?
If it goes up and down okay but not enough, try this.
Remove screws holding the receiver in. Loosen bolts. Put lockdown bar on. Tighten bolts and put screws back in.
If that doesn't do it. You may need to make the holes on the receiver longer so you can move the receiver more.
LTG : )