Be careful sticking to a formula for elevation. 1 inch equaling 1 foot is a good rule of thumb but the loft of the club has a lot to do with it. A wedge isn't going to be as affected by an elevation change like a longer iron would be. You have to envision where, in the final 1/3 or so of the ball flight, the elevation interrupts the flight.
Bethpage has a number of good examples. The 15th is all elevation at the end of the fairway. Get close enough and you can put a wedge close to the pin. From further back you have to use a longer iron and because the arc of the shot is so flat you have to add clubs. Then you're coming in like a freight train because the elevation interrupts the flight before it reaches the full distance and turns it into a ferocious roll.
Look at the replay of shots like this after you make them and you'll get the picture. Go ahead and subtract the yards from a drop in elevation and add them for an increase but also pay attention to how far away the elevation actually changes and the club you have to use to get there.