block only placeable on walls not working

i've got a block in my mod that i'm trying to only be placeable on walls, and i've done this by adding a valid placement condition that checks if the location is a valid position for a ladder, and if so, it places the block

however, when i try to place it in game, it doesn't work and can only be placed normally facing south. east and west require a block to be placed to the left or right of the block to work, and north requires a block in front of it. i don't have any other procedures that would do this, and any help would be greatly appreciated

edit: i've just given up and decided to make it placeable on the floor and ceiling, but it would still be nice to know what was up with this