Split Gang Fitting Family - Revit MEP 2012

[TwistedTLM4]

I've taken a stab at trying to create a parametric duct fitting family pictured below with limited success:

Split Gang Fitting.png

Parameter Info:
Duct 1 Width and Duct 1 Height would be manually entered based on what is required for the airflow.
Duct 2 Height and Duct 2 Height would be equal to Duct 1 Height.
Duct 2 Width would be manually enter, while Duct 3 Width would be equal to Duct 1 Width minus Duct 2 Width.

I will preface this with the fact the I started with the "Rectangular Elbow - Mitered - Single Thickness Vanes.rfa" from the Imperial library in Revit MEP 2012. I went through and added the extrusions, parameters and constraints in order to accomplish the above mentioned results. The fitting worked for the default dimensions that I entered in the family (Duct 1 = 24x12, Duct 2 = 12x12, Duct 3 = 12x12); however, when I load it into a project and modify the Duct 1 and Duct 2 dimensions, I get the results shown below:
Split Gang Fitting-Result.png
Any insight or suggestions as to what I'm doing wrong?

Attached is the .rfa for anyone who wants to look at it.

Thanks,
Tony

[TwistedTLM4]

Bump! No suggestions?

[tim.winnington852413]

Tony,

The bend is doing some funny tricks but to resolve your issue try to build you geometry so it is aligned to reference lines and locked and the dimensions are then adjusting the reference lines. Hopefully the mod version will give you the idea.