Did you know you can use parcels objects as a boundary? I didn't so I decided to play around with it. I found adding parcels objects didn't quite work as I expected. You can only select one parcel object, which I find a great limitation. When you select a parcel label the boundaries of the parcel are highlighted. I would expect the ability to select the parcel label and have the boundary of the parcel added as a boundary or when you select multiple parcel objects, have the computer see if they made a closed shape and add the resulting closed area as a boundary.
You can also use a polygon as a surface boundary, though I haven't quite figured out what that means. The help just mentions polygon without indicating what type of object they are referring to and the Developer's Guide gives an example of a circle. I did try using AECPOLYGONs and MPOLYGONs as a surface boundary and both didn't work. I used the polygon command, but that just creates a polyline.
Another thing abound surface boundaries I learned is that the parcels objects, polygon or polyline doesn't need to be closed. The program will automatically close the boundary by connecting the beginning and ending points of the added boundary.