I'd like to make a vertical slope less steeper than 45° (no slope block then). The issue is that the collapsible block can collapse only the upper and lower faces but not the sides one.

Here is an example made with an horizontal slope, what I would like to accomplish is the same but going vertical (pick the image and imagine it rotated 90° clockwise.

Is there a way to do this with the collapsible block?

EDIT:
While doing some test I also noticed that right clicking on the side of a block with a collapsible block in hand won't place it.

Using the 3.3.7 version.

It probably requires a solid face to place the block. The collapsible only has up/down variants, so what you're looking for isn't possible at this time.

Thanks for the clarifications ;)