How to get instance driven parameter value of detail item family from current project document?

I’m trying to get the instance driven filled region area from a detail item.
I have no problem by using FilteredElementCollector(EditFamily) to return elements and parameter form the family Document. However the parameter value is only for the family Doc but the current project doc. Like the images shown below. the scripts always return the value of 3x3 box from the family editor regardless the instance value from the current project document.
Is there any ways to get the parameter value that present in the current project document? Thanks
In Family Editor:
In Project:

Could you just grab the L and W from the instance and do the math rather than getting the region and then it’s area?

yes, but what happen if there are more complex geometries to handle.

As long as those geometries are being drive by parameters you can calculate the area. The problem as you have found out is the only way to get the nested region is by editing the family, but instance parameter information isn’t available in the family editor environment like you will want and are experiencing because the instance parameter just has a default (3x3) and not the project (5x5).

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