The help topic that concerns the definition of mass Eccentricities says: "If stories have not been defined in a structure model, the Eccentricity is calculated based on the global dimensions of the whole model."
Which are the "global dimensions of the whole model" in order the values of Lx and Ly to be calculated? Are they the distances that correspond to the base of the structure (where the structure is supported in the ground) or are they coming out from the distance between the outer nodes of the structure (that may belong to an upper level above the ground)?