Pyramid Corner?

We are aware that there is a flat plate at the corner of the pyramids where rungs meet. How far from the corner do they extend?

The best way to try and answer your question would be to refer to official drawings for a typical section of the plate and leg. Please go to;

http://www.usfirst.org/sites/default/files/uploadedFiles/Robotics_Programs/FRC/Game_and_Season__Info/2013/2013_Game_Specific_Drawings.pdf

And then find Drawing GE-13020 sheet 1-5