This is hard to address without more information. My first guess is that the Shure could be right because it uses a two point (the two null points in the stylus' arc) system that allows you to triangulate to find the location of the tonearm pivot, versus the SME which has only one point (and presumably assumes the correct pivot location).
I note that the SME 309 typically comes mounted on a "sled" sliding device that permits adjustment of the key tonearm pivot-to-platter spindle distance. Perhaps your arm is out of adjustment.
The SME web site is: http://www.sme.ltd.uk/html/series300.html
This web page identifies the correct pivot-to-spindle (center of spindle) distance as 213.4 millimeters for the 309. If you think the distance may be set incorrectly, I would urge you to measure it and see if it is close to this number. If not, it is likely you can adjust it using the "sled" apparatus. Good luck.
I note that the SME 309 typically comes mounted on a "sled" sliding device that permits adjustment of the key tonearm pivot-to-platter spindle distance. Perhaps your arm is out of adjustment.
The SME web site is: http://www.sme.ltd.uk/html/series300.html
This web page identifies the correct pivot-to-spindle (center of spindle) distance as 213.4 millimeters for the 309. If you think the distance may be set incorrectly, I would urge you to measure it and see if it is close to this number. If not, it is likely you can adjust it using the "sled" apparatus. Good luck.