Yes, that's correct. There just isn't enough flat surface area at the top of the slide to mill the rail style footprint without cutting into the internal firing pin channel inside the slide which would render it not safe to shoot. So alternative would be the Trijicon 1911 RMR adapter plate, with the RMR to 509T plate on top of that in order to mount the 509T. We wouldn't recommend that route, it's overly expensive, and it adding a lot of weight on top of the slide. Wish we had a better solution for you but, options for the SP-01 are limited to the narrower optics.