"An Example of the two ways that Concrete Walls can 'snap' to Floor pieces, one way that it can align is shown highlighted in Red (where the Wall piece can overhang off of the Floor piece) and the other way that it can align is shown highlighted in Blue (where the Wall piece can be flush with the Floor piece). Both can be helpful in lining up connections utilizing Concrete, or with creating a specific 'look' [neither is really 'wrong', IMO].

Created initially for a Steam Discussion talking about wall alignment; if alignment in your Settlement is a concern, be sure to check this behaviour [that seems specific to Concrete].

HTH
~Tesityr"