That looks correct to me. Are you using the Core or Studio API? Geometry occlusion only works with the Core API- to use it with FMOD Studio you would need to poll System::getGeometryOcclusion and use the direct and reverb values to drive an FMOD Studio parameter controlling volume, filters etc to create an occluded sound.
System::getGeometryOcclusion can also be a good way to debug your geometry, if you place your geometry between your playing channel and listener and find that the direct and reverb are still 0.f then your geometry might not be where you think it is. In such cases, try matching the geometry of your world by using global vertex positions in your polygon instead of their local position, and leave transform, position and rotation as their default values.