[Connect U11] Contraining an extrusion along a path

I'm testing constraints with an extrusion along a path to create a door frame. I want to constrain the height and width and have them as variables but when I attempt to 'flex' the variables the results are inconsistent and wrong. I've created the constraints by constraining the path before extruding as I can't see a way to do it afterwards. The height constraint seems to work but the width is giving odd results. Example attachedperforatorNamedViewtest.dgn 

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