Shotout - A lot depends on your material - grain, temper etc..
For a simple part like yours we would take a piece of CRS about 1 1/4" thick and bore a 2.250 dia hole. Cut it in half and provide an adjustable stop on top. Now make a first blank with the dim.s available. Keep a record! Locate the blank on top against the stop and press down with a 2" dia bar (punch). Now see what you have and adjust from there by making a new blank and moving your stop. Mounting all in a die set would be one option.
If you need to bring in the sides - bore a smaller than 2.25" radius on the bottom of the die, kind of like a small dip in the center and you may also cut down on your 2" dia punch. It is actually easier than it sounds. A few blanks - try and adjust. Keep records of your blank dim's. Case harden.
One alternative would be to leave the blank longer and trim in a secondary operation after forming.
If this is a die for a large production run you would want to invest in a book on forming dies. Here you will find a formula that will get you close, but you will still be making some blanks to get to the right size for a developed length. You could be looking at a draw die with pinch trim action or even a forming die using a urethane rubber cushion and just a forming punch. You will need a good size hydraulic press for this option.