[bjt]

But who's to say they're descending rather than ascending?

A person can ascend stairs, or descend.

A drummer could play an ascending pattern on their toms, or a descending pattern.

But neither the toms or stairs have an inherent upward or downward direction.

[Cogito]

I took it to mean the toms were descending towards the ground like stalactites descend towards the ground - they used to be shorter and now they're longer.

[posterboy]

that is after you read the article, correct?

[Cogito]

Correct, before reading I presumed it would be about tone.

It’s possible the title is a bit of a pun, and refers in part to both tone and shape.

[adrianmonk]

I guess the way they mean it is not about playing. It's about how, as your eye moves from one tom to the next, you see the bottom of the tom's shell getting lower.