creating/modifying network surface

Hi there,

I have created a surface from which I want to modify the boundary. See the screenshot attached.

The green curves show the existing boundary, while the red curves show the boundary how I want it to be.

However, patching these curves give a really weird result. Unless I set the flexibility higher, but then the boundary is not constraint to the building (shown most right in the picture).

Using the network surface doesn't work either, since the surface has six boundary edges instead of 4. So I'm thinking the best approach is to modify the current surface edges, but I can't figure out how to do it.

Any hints are appreciated. A rhino file is attached.

Regards, Rutger