Expressions belong to properties and properties can belong to only one element.
Elements can not interrogate the same property from other elements, so you can never get a total.
You have to create a 'Total' property that you manually type in the total area, then you can associate this total property to all your morph elements and can then use it in an expression to calculate percentages or other relations.
Or you need to delve into Python or C++ addon creation to gather information from many elements.
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Versions 6.5 to 25
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