Lowered ceiling for half a room

[Mainer]

As you can see in the attached, my main floor garage floor is about 6" lower than the adjacent rooms. The floor system that supports this garage is very thin, which is unrealistic. I think the software is giving it a 4" slab instead of 12" floor joists. In reality I'll probably have at least 12" trusses supporting the 4" slab to carry the two vehicles. The full width room below is my basement garage-workshop. I'd like to depict that half of this room will have a lower ceiling due to the support the garage above will need. I believe my only two options are either an invisible wall and setting the ceiling heights differently, or placing a full width and depth 12" soffit at the basement ceiling to represent the ceiling trusses.

I'm leaning to the soffit idea but wanted to get other opinions. What would you do?
Thanks.