Elliptical Cap Quandary

Hi,

I'm trying to put a cap on this part that I've constructed by offsetting a sketch line, extruding that form, then filleting the top surface to produce a full round.

When I add a half-ellipse to the end of the sketch to be extruded and fillited however, it does not produce this same full-round result.

I can approximate the shape I want by creating a boundary surface, but then this part of the form is hollow when I need it to be solid...

This is on SW2011 btw.

Any thoughts on how to properly make the form I'm looking for?

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