"I know it can not be the project's plant ground elevation because Caesar would not know this." Well, let Caesar know it and check the global coordinate of your first node - make sure the elevation of your model is "correct" vs wind definition.

About ASCE 7-16, there is a coefficient Ke Ground elevation factor indented to correct the air density considering your site elevation vs sea level (but often is taken as Ke=1) and a Velocity Pressure Exposure Coefficient Kz which considers the effects of gradient of the velocity in the boundary layer "above site ground".