[jaykay]

There are ajustable stops at the front leading edges of the clamshell. This will take care the front edges obviously. If your rear edge is up I would look at what might be interfering with it going down there are stops there but I have never played with them.

A half an inch is quite a lot I would say something is sticking or gone asymmetric on you. Look at mechanism function first rather than down position stops adjustment