Well it might be also a language issue (I am not a native English speaker), so you might as well leave it as it is, if you think it's good enough. But IMO points which are not clear enough are that:

• brick base is large enough to fill the bottle diameter entirely,
• I'd associate the name of rimLength with some kind of circumference (bottle neck opening circumference, maybe?) rather than distance.

Maybe I'd go with something like:

_A magician in the subway showed you a trick, he put an ice brick in a glass bottle to impress you. The brick has a shape of a cuboid, and its base is a square as large as diameter of the bottle allows. You have no idea how magician managed to squeeze such a large brick through a narow bottle neck, and now he threatens you that he will turn you into a frog if you do not calculate it's volume! Fortunately, you can use your headphones cord to measure some things: bottle radius, bottle heigth, height of a part of a bottle which is not occupied by the brick (or maybe: [distance / height of a bottle remaining] between top of the brick and [bottleneck opening / bottle rim / top of the bottle / idk...]. Write a function iceBrickVolume that will accept these parameters:... _

As I said, English is not my first language, so you might ask for help on kata-authoring-help Gitter char.

Sorry for that. If you can suggest something more clear I'll be happy to update it! Thanks!

The kata is cool, but I lost more time trying to understand the discription than coding the solution.