The reason for this - there is a mod that allows for vertical placements of any slabs so your variants, sorry for this, aren't needed. Full slabs has this advantage where you don't need another crafting recipe because you just craft a slab and you can place it both horizontally and vertically.

Vertical Slabs Disabled added 0.2.1a

add mbmconfig.json to the mods folder with this as the contents

{
"vslabsEnabled": false
}

"vslabsEnabled": true - Means vertical slabs are enabled
"vslabsEnabled": false - Means vertical slabs are disabled

Command added- /mbmgamerules verticalslabsenabled [true|false]

This will automatically create the file and set the value in file. Also changes the value when command is run at any time.