elongated toilet seat

We have a Toto Ultramax MS854114SG-01 and just bought a replacement soft close seat number SS114 just like on our Love Plumbing 2005 invoice. It is not quite the same shape. It is elongated but not as pointed. It maintains the edge thinness all the way back to the tank, but the hinge area...

Please help me. What causes a toilet lid to bang into the tank when someone sits down? I just moved into a house and decided to change the toilet seats. It is a Toto Elongated Drake model ST743S or ST48S (hard to tell). I have tried several soft close and as soon as anyone sits down, the lid...