Smart Art re-sizing issue

I often need to use hierarchies in presentations and documents (word or powerpoint). The smart art function seems like a dream for this sort of thing, however, it never works. Anything more than the simplest graphic is hopelessly mis-sized.  The problem is, as you add more layers, the boxes and the size shrink. When you attempt to change the size on one box (eg make it bigger), the other boxes change (become even smaller) relative to the first box. It is like some sort of cruel joke: the more you try to fix one box, the more jumbled the other boxes become. A hierarchy would be far more useful if you could adjust the sizes of individual boxes to show their relative importance or to emphasize a particular part.

There must be some way to lock the the size/position of part of the graphic or to adjust only specific parts without effecting the others. If not, then this "tool" strikes me as completely useless and I wonder if anyone anywhere in the world ever uses it? I have not been able to find any help any place else, so this is my last hope.