Well the BrepFace.BoundingBox was not giving me a bounding box of part of a face after split, but rather a box of full surface. This was the reason to create this post.
I think I got correct results after I’ve used: face.DuplicateFace(false);
All in all I made it run, but I need to work on my algorithm, because a split of faces and selecting proper faces takes too much time.