One aspect that contributes to the very high legibility of the Latin alphabet is that the letters have ascenders and descenders which creates a characteristic silhouette for different words. This way, a word can even be read when the top or bottom 50% is cut away. Additionally, it speeds up the reading.
In Japanese, all characters have the same height and no ascenders or descenders. Sometimes, Kanji are set bigger than Kana which improves legibility. But writing kana with ascenders and descenders is uncommon.
I saw it written that way on a beer ad in the Tokio metro, ハ was as big as x, some characters were descending like p and some ascending like h. I unfortunately do not have a photo of it and forgot which characters were higher and which ones lower.
Is there a preferred way of setting the kana like this? Which kana should be x high, which ones cap high and which ones descending and which ones ascending?
"That concept doesn't exist in Japanese". But it is being used and does improve legibility. We don't have to do something the way we always did.