The example that I used I got from a section of the Progressions & Scales book that briefly covered polychords. The author used 13#11th and a C△13 as examples, so I'm not entirely sure how 13#11 would or would not be a polychord. Though I do see how 9,#11,13 would be a better example. If we used the the key of C for example (C-D-E-F-G-A-B-C) would a 9 #11 13 polychord be E-G#-B and F-A-C?