By default, setback lines are not included in your site boundary, as all setback distances are set to 0. You can specify a setback distance for each individual site boundary edge.
To define setback distances:
Click on the property line you want to specify a setback distance for. Note that setback distances are defined per site boundary edge, one at a time.
Right-click and select Properties, or select Edit > Modify Elements > Properties.
In the Site Boundary Edge dialog, edit the value in the Setback edit box.
Click OK.