How are cross-linear abilities positioned through smartcast?
These walls that you mentioned do not offer any more options when you place them, only position.
Even without smartcast, you can only click where you want to put it, The angle is decided where your character is facing / The relation of your position to the position you want to place the Wall.
Abilities which can be placed by setting a position and an angle ( Like Rumble Ult) , offer these options through a drag mechanic, which is present in smartcast as well.