How to use geopak drainage to model/design roadside ditch/median grate inlet?

Happy MLK day, everyone! I need some help on the following question.

A grate inlet in a roadside ditch or median is basically in a sag to collect runoff from vicinity area/ditches coming to it. But how do I set it up in Geopak Drainage? I can model it as a regular sag inlet but then I realize it is different from a normal sag inlet at the pavements (for example, it does not have spread section, and most of time it does not have the same right/left slope as PGL). any hint? Thanks.