I don't think that rack is meant for your frame. Looking at websites that sell the rack, the Disc Rack mounts to a unique surly brazeon on bikes with a "traditional triangle" about 1/3 up the tube.
It looks like the design of your "triangle's" was intended to be used with more traditional racks and not need to use the Surly Disc rack.
Just my opinion from where you are mounting the rack compared to other pictures on the interweb.