3D textures with Xray problems

Hello,
I have a problem (I don't think I'm the only one in this case), I make 3D textures for a map and for some versions (I know that in 1.12 it worked) there are no more transparent faces on all sides of the stairs and slabs which were very handy for 3D textures.
Now, the textures look like on a normal block, there is very annoying xray. There are not a lot of directional blocks with all the transparent faces ...
What would be good would be either to put as before, or even better, add an option in the 3D model files allowing to put the transparent faces on any side of any block.
Thank you in advance.