Mass Properties Analysis: Assigned vs Computed

Hello,

I have to provide moment of inertia and COG information for our products (avionics boxes), this was done by a consultant previously.  Since a number of circuit cards exist in the model, there can be thousands of parts that I don't want to provide materials to individually and instead I will weigh the card and provide an assigned mass to the assembly level of the card (a bit of corner cutting here).  My assumption is that Creo takes this mass and applies an even density through the assembly.  There are also other instances where I am working in other people's models and they have parts that should not be included in the analysis, but are parents to a number of parts that must be included.  Not wanting to fiddle with the model, I also assign negligible masses to these parts.  I'm assuming that this negligible mass is now practically invisible to the calculations.

My issue comes when I attempt to run the analysis with the assigned masses.  The total mass comes out accurate, and the center of gravity seems right however the inertia calculations are clearly wrong.  Based on some simple hand calculations I should expect values on the order of 20-100 lb*in^2, however I'm getting in the 10^7-10^9 range.  This is similar to what I get when running the standard computed mass analysis so I feel like creo is doing something with the default values and not the assigned ones.

How does Creo calculate these values when using the assigned values selection?  Is there a method I should use here instead for ensuring assigned values work properly?  Or am I missing something more fundamental?

Attached is a text file of the results of the assembly analysis, both the computed and assigned values versions. 

Thank You!

-Joe Seymour