if you want use the X axis for your stop, and on the stop "finger(s) or Plate", put a limit switch that when the sheet is all the way back, the one or two switches are your confimation that the sheet is fully against the rear stops as a check.
further, if you want to control bend angle, AND you do have on/off control of the press hydraulics (should be a soliniod), you can make a data wizard, that can take into account the thickness of your metal, (bending tool type if neccessary), and how much to push (with a spring back adjustment), for set angles.
scott