If you want to put the text INSIDE the shape then you will need to work out a scale that works for both the smallest and largest sizes. You will have more flexibility if the text is sitting beside the shapes or your shapes are using a more complex formula to set absolute minimum or maximum sizes. For instance, your shape's height could be set to
where Prop.Width is a Shape Data Field, 10mm is the minimum size of the shape, 100mm is the maximum size of the shape.

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Andrew Lockton
Chrysalis Design, Melbourne Australia