Since the day it was released there's been a fatal flaw in the Tinkercad Shape Generators API that make the use of generated shapes challenging and error-prone, and the writing of new scripts unwise until this inconsistency is corrected.
Create a new design.
Add a MetaFillet SmartShape object.
With the object still selected, note the ‘height’ parameter of this smart shape.
Using the shape's standard on-canvas controls, increase the height (tallness) of the fillet to 50mm.
Note that the inspector of this smart shape shows a value for the height parameter to be the original value (8mm for me), yet the actual height of the object on the canvas is 50mm.
The team has been aware of this flaw all along. You've acknowledged it's existence and significance. It's time to fix it so that users get an accurate and consistent readout of a shape's size.