" Can' t place wall if there is one item nearby. "
You actually can, just make sure that you dropped that item on the wall grid perfectly, but you gonna need this mod :
https://steamcommunity.com/sharedfiles/filedetails/?id=1601725838&searchtext=action
And enable drop on grid from settings, place 3 piece of wall as u did in this screenshot:
Place your character in the middle and shift + right click to drop that item perfecly on the grid. That will allow u to place the 4th piece of the wall.