Sorry, I don't know any way that would make it possible to list in a Column Schedule a Column Segment geometry parameter.
The only thing I can think of is to create a Property for the Column, which would be a Length type Property, enter for its value the value you have specified for the thickness of that Column base, and schedule that value.
Of course, this is not automatic, you have to specify the value manually, and if that Column base thickness value changes, you have to modify the value of the Property as well.
Not very BIM-like but at least you can schedule it.
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