Volume discrepancy question

I modeled a multi-part model in Unigraphics, which can calculate the volume of your model. When I compare my calculated volume to the volume shown on Shapeways when I upload it, they're not the same. What am I missing? The volume shown on the site is like 18cc MORE than my calculated number.

Here's the model: https://www.shapeways.com/model/737734/b0f0c61eb2857af67ad19c e4fafaa7e8

My calculated volume is: 198 cc

Shapeways volume shown online is: 216 cc


Why does it show more? I've got a lot of hollow volumes in it, but they've all got drain/access holes, so there's no captive holes. Any ideas?

Normally I wouldn't care too much about the volume, but this is a pretty big model and I was being very judicious with volume to keep cost down, but now it doesn't match my predictions, and it costs more than I expected.


Thanks!

~ Ben

UPDATE!

I fixed the volume discrepancy problem - I had a hollow void that I forgot to add a drain hole for. So now the volume matches exactly, but I still get an error-email telling me that my model is too big; which I KNOW Is bogus because I modeled it to fit in the WSF bounding box.

Do our uploaded models have to be in a certain orientation for the auto-check program to work? Like, maybe it's too "wide", but if you rotate it 90° it would fit being "tall"?

ANYONE?!