think of it like this. if it's 18m and he's doing a 360, then that means he is already halfway done with the trick and only a few feet from the lip.
Which means he is going to be flailing like hell for the rest of it, if not crash.
Alot of times people will put that a table is '60 feet big' or whatever, and be referring to the start of the jump and all the way down the landing or whatever.
If its at a national championships they're not going to have a 10metre kicker. I think it is 18m, you can't pretend to judge it cos you can't see the landing.