Tapering cut on a bell shaped piece

Hi guys... I'm stumped and was hoping someone here could help.  I have this tapered, revolved piece (think bell shaped) that I want a decorative cut on.  At the base (wide end of the bell) I want the cut to be thicker than at the top.  What would be the easiet way to do this?  I'm clueless when it comes to surfacing, so please dont recommend that.  Attached is the file so you can check it out.  I'd like the bottom cut width to be twice the top cut width.

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