To unify the form and the internal wall in a 2D section

Attach the same part to the form as the part attached to the internal wall or attach a part to the form which is in the same unify group as the part attached to the internal wall. Make sure that Unify is on for the unifying part and that select 3D from the Add To option menu.
If select 2D, or 2D and 3D, the 2D representation of the form appears in a horizontal section through the frame. It appears as if the cavity closure and the internal are not unified.
Turn on Always Generate 2D for the part attached to the form. To set this option: edit the part which is attached to the form, select Attributes from the Category list, and turn on Always Generate 2D. When calculating a horizontal section, the form is cut in the same way as a normal form. The result is that the section through the form unifies with the section through adjacent walls.