Modeling of Built Up / Tapering Columns

Is there a guide as to how to model a built up column in Ram Elements with various section properties across its height? 

I'm looking to design a column that has changing section properties across its height. It would not be linearly tapered but more like a hot rolled section fastened to another hot rolled section for only a certain height. ASIC Design Guide 25 provides guidance as to how to analyse non prismatic sections in compression. When I try to duplicate results in Ram Elements they do not match since the K and Lu in Ram Elements does not account for multiple section properties for buckling, or at least I'm not aware as to how to properly model such a column and capture its buckling behavior properly. 

I see there's a section for built-up members under compression but even when altering the fastener spacing I still get the same capacity.

Please advice if possible. Thank you. 

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