You can apply custom planking on individual levels.
To do this
Click on a Bay, and select More on the level you want to apply the planking to

By default, the width of the planks are 19cm, and we change this level to 32 cm.

Select Planking (custom)

Change the Width to the required length

When done, click Apply

We can see that the first level uses fewer planks than the top level.
