When I design my network, I am getting an extremely small value for spread for the sump inlets. The calculated spread for the on-grade inlets is correct.
This problem is probably related to an incorrect Oriface Depth setting in the structures.dat file. This user-defined value determines whether a weir or orifice condition exists. The software compares the orifice depth to the depth of flow in the gutter plus depression or sump depth defined. If the depth of flow in the gutter is less than the defined orifice depth value, then the equations for the weir condition are used. If the depth of flow in the gutter is greater than or equal to the orifice depth, then the equations for the orifice condition are used. (This parameter is used for all inlet types except Curb Opening Inlets). This user-defined value is used in the design phase only.
Note: Curb Height, Curb Opening Height, Curb Length and Orifice Depth settings are stored in the structures.dat file. The settings on the Tools > Drainage > Options > Design tab are used only when loading old structures.dat files that do not have these settings stored. New structures.dat files use settings from this tab.
You should edit the Oriface Depth by going to Tools > Drainage > Structures File. Set the Structure Type to Inlets. Select the Inlet and Size that you wish to edit and change the Oriface Depth on the Edit Size dialog.