Hi @mi.land the building boundary is not meant to be used for clipping the model for specific details (imagine if you needed to show different details of the same project).
However, even if you define a small building boundary like that, the section cuts should appear fine in the page layout. If you can share that file we will revise this and fix any possible bugs.
I suggest you to use VisualARQ Sections to show the model clipped by one specific area or detail. With the section end points and the depth control points you can control the area by which the model will be clipped. And you can use the levels visibility to clip the model from the top and the bottom: