There are only two Merchant Parameters on the Elavon tab: Terminal ID and Merchant ID.  The Terminal ID actually has two values in it.  If you hover the cursor over "Terminal ID", in the file you will see a pop up that states "6 digit Bank Number + 16 Digit Terminal Number."  When you build the file you must enter both of these values in that one parameter.

BroadPOS Parameter Name            Elavon Parameter Name                          Number of digits

Terminal ID                                        Bank Number + Terminal Number          22 digits

Merchant ID                                      Elavon MID (Merchant ID)                      10 digits