We installed a Nexus toilet and the softclose seat (elongated). The plumber hasn't worked with Toto products before. The seat moves side to side somewhat. We looked at it and the back piece seems to be tight, but the the seat moves. Is this usual for the softclose or is there something that needs to be tightened more that the plumber missed? On another note, this plumber was not happy installing these because they were "different" than the usual American Standard, etc.