The inside surface is flat straight accross. The only cut out areas are two very shallow scalloped out areas from just behind the plate screw hole to the rear edge. These are perhaps only .015" deep (just my guess) and give some clearance to the sears .
The plate is dome shaped on the outer surface of course.
It's perhaps .175"+ thick at the center and around .100"+ at the edges where it sits on a supporting ledge in the frame cut.
All this can vary, especially on a gun that's been refinished.
But generally speaking it takes quite a wack to inwardly dent the trigger plate.
In the wrong spot it could effect the sears. Maybe the hammers,,but that would one bad ass dent.
The frame at dead center and right in front of the trigger plate on the bottom is often dented inward.
The frame is very thin right there for about a 1/2" length alongth the trigger plate edge.
The dented frame comes often from the use of a hammer in the re-installation of the Fox guns hammer & mainsprings. A few hits and a few misses and that fragile spot on the frame dents inward easily. Plus the 'hammer the hammer' method won't get you anywhere in the installation process.
The trigger plate does a lot of stuff including pulling the frame assembly tight to the stock when the tang screws are tightened.
That slanted surface on the front of the boss that the triggers pivot on is what does that trick as it is forced against an opposing face in the butt stock.
Without it, you'd be depending on the tang screws to hold the frame tight to the wood,,,,like in an Ithaca Flues.
