This is the best article about 13 foot jumps. James White is the best one-leg jumper in basketball I have ever seen and his stuff is well documented. In general he was closed - about 2 inches short (and there is a video in youtube).
- look at 0.47 mark !!!
To comments both Dwight's and White's attempts:
- Dwight jump of two feet and straight to the backboard- so he twisted his body a little and still touch 12 ft 6";
- James White - reported Olympic caliber high jumper in university, maybe lost 1 or 2 inches of his athletic prime (which is normal, given the fact that people athletic primes is usually between 20 and 24 - after 27, 28 you start lost a bit. But I am sure (as the author) that several years prior to that attempts he was capable of reaching 13 ft.
And another guy on bad quality: