xsys, ysys, zsys = "3" treats the coordinates as "% of the graphics area", therefore x=20 is treated as 20% of the way from the left side of the graphics area, etc.
Since you are using actual (data) values as your x, y, z then you will want to use xsys, ysys, zsys = "2".
-----
For more info on the xsys/ysys coordinate system values, the following table might help:
http://support.sas.com/documentation/cdl/en/graphref/63022/HTML/default/images/annodata-fig3.gif