It just seems odd that they don’t and although WK plays fast and loose with radicals/stroke orders, it bugs me that lid is there since it is more accurately described as drop, ground, water with they way they’re both written.
I would say 球 should just use Request, which already is a radical, but level 31.
I feel as though maybe Koichi’s chosen the specific radical fragments to yield the best mnemonic. In the end, the purpose of the mnemonic is to act as an aid to help you remember. If it’s not helping, come up with your own mnemonic - a self-devised mnemonic is the best mnemonic.