Well, the mnemonic is intended to help you remember the radical (and the meaning). If they’re not working for you, then feel free to come up with your own. The best method is the method that works best for you – if Koichi’s method isn’t working, then toss it out.
You can toss the meanings too, if you’d like. The radicals have “meaning” only because they come from other kanji which each have their own meanings. For example, the left hand side of 校 is 木, which means “tree”, but only because the kanji 木 itself means “tree”. Some radicals do tend to lend their meaning to kanji that they’re in – for example, kanji containing 水 or the radical that Koichi calls “tsunami” (but which is actually just a compressed, radical version of 水) tend to have meanings relating to water or liquids (水 = water).
For that matter, Koichi has just invented some of the “meanings” out of whole cloth. The radical that he calls “fish tail” is actually the compressed radical version of 火 = fire.
In summary: the meanings and mnemonics are just a stepping stone to help you learn the radicals, which in turn are just a stepping stone to help you learn the kanji. If the stepping stone isn’t working for you, come up with another. =)