Why should the couplets on the window be engraved with sixteen words, such as "The moon is high and the moon is small, the truth is clear" and "The breeze is Xu Lai, the water waves are quiet", but no

Why should the couplets on the window be engraved with sixteen words, such as "The moon is high and the moon is small, the truth is clear" and "The breeze is Xu Lai, the water waves are quiet", but not other words? The miniature sculpture of a nuclear-powered ship described in Nuclear-powered Ship is a scene in which three friends, Su Dongpo, Huang Tingjian and Fo Yin, take a boat trip. Of course, relevant allusions should be engraved. Among Su Dongpo's travel notes, the poem "Ode to the Red Wall" is the most popular, so the best story line in "Ode to the Red Wall" is chosen to be engraved on the window of the nuclear ship. "The mountain is high and the moon is small, and the truth comes out" comes from Houchibi Fu, and "The breeze is Xu Lai, and the water waves are quiet" comes from Qianchibi Fu, all of which describe the scenery of watching the moon on the river in autumn. "The breeze is Xu Lai, and the water waves are not good." Autumn dusk, the genius is dark, and the moon is not out. Even the wind has become gentle, the waves are rippling gently, and the river is quiet. "The mountain is high and the moon is small, and the bottom is crystal clear", which means looking up at the cliff from the ship. In the dark, the mountains in Cui Wei are very high, and the moon looks smaller and smaller. Is it because autumn comes and the water level of the river drops, so the mountains are particularly high and the moon is particularly far away? This kind of scenery-writing sentence is carved on a small nuclear ship, as if the people on this ship are not in the showcase of the museum, but traveling in the reflection of the clear autumn river and the moon, which suddenly gives this microscopic still scene an infinite magnificent background and broad imagination space.