The mortar has been floated up the wall on the right hand side of the shower stall (viewing from outside the shower stall). You can see how the mortar, once floated into place, really evens out everything, especially these recessed shampoo boxes that are part of the shower stall.
You can see a corner of the bench seat at the bottom of this picture, and the excess tar paper sticking out behind the mortar on the right hand side.