The Coord@ comes in to play when you are getting the values to run a query not using the web interface. It also seems they have upgraded the interface a fair bit since I used it first. In Vector mode, you could not set the SSB as an option for the center, or at least, it never seemed to work when I attempted it. I think it also pre-filled in the coordinates when I first used it, although it is hard to know what a website did in the past, especially one that saves the last query you did. It is possible that this was also set because I searched for a target from the list of cities, which might have pre-populated the observational location. If you have the coordinate filled out for the object type, and look at the "Batch" mode configuration, which was my starting point, you get the following:
STEP_SIZE= '1 d'
coord@10 is the
coord@ I was referring to. By looking in to the documentation, and taking advantage of updates they seem to have made since I first was playing with the interface, I discovered I have much better results without the "coord" in the center, as it won't track a point on the sun, but rather the center of the sun.