The only requirement for the home point is that it is in a position that the motors can hold still. So the angle of the cord going to the gondola is the thing that really matters. That's why very wide machines usually have lower home points.
You need to set your mmPerRev. As stated, this is the amount of cord that the spool will let our in one revolution. It is not the diameter. If your bobbin there is a standard sewing bobbin, then the core is probably about 8mm across. However, since the cord is so thick and the bobbin is so small, the diameter of the core of the bobbin will change rapidly as line is wound on and off the spool.
10mm diameter might be ok as the average. Now, when you unwind that spool one full revolution, you'll find about 31mm of cord is let out, so your mm Per Rev is 31.
Note that you will never have a very accurate machine because the diameter of your spools will be changing constantly with such small spools and such a large machine.
You have your machine set to 1450mm wide, so your motors must be 1450mm apart from one another. Because your cord is leaving the underside of the spool, your distance measurements should be from the outside edge of the spools. The 1300 is the size of your paper, and is not a relevant measurement for calibration.
Your drawing is skewed to one side, so this shows that your centre line is not actually central. It should be exactly in the middle.
Your stepMultiplier is set to 4. This is unusual. This depends on what microstepping setting you have configured in your firmware and your hardware.