Don't take anyone's word for it -- measure the effective width of the implement and write that down and enter it as the swath width in the 250.

Now go out in the middle of an unworked field and set an A-B that runs pretty much north and south. Get on that line, engage EZ-Steer and when it gets to going straight, put the implement in the ground and work for 10 feet or so. Raise, go far enough so you can turn around and get lined up on the same A-B, and 10 feet before you get to where your first pass ended, lower the implement. When the two passes meet, stop, get out and measure how far the passes are offset. Take that distance and enter half of it as the implement offset in the 250. Trial & error will tell you if you should have entered the offset as left or right. Repeat the exercise until the passes meet with the desired precision. I usually quit and write down the number when I get within an inch.

Of course, your results will no be good unless you have done a proper and accurate roll-cal on the EZ controller. You also need to be fairly accurate on what you've entered as the antenna height.