Column of scaffolding are only ascent (not down, just up) when the "support" is a scaffolding block "above" the air.

In the previous structure, all the blocks of the scaffolding column have the appearance and operation of the scaffolding blocks on the air.

In the commented structure, I expected the player to be able to go up and down, and when the player goes down, stop at the block that is above the air.

In the 2 cases (up and down, in the 2 structures), the speed is very low.