I think you should be able to do this using the Parameter Script of the GDL Object. There you should create a formula or conditional statements for how the height should change based on the length change and then assign the result with the PARAMETER command to the Height parameter.
I have not tried this but I think it should work.
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Thanks for the advices Lazló.
I got a solution for this case - I did a combination beetween Parameter and 3D Script statements. Soon I will bring results.