Question about Bounding Box Limits

Im trying to find this information on the site, on the materials gidelines and on the tutorials but I cant find it.

I have this model, https://www.shapeways.com/model/1143420/rikipeke02b.html very big and flat. It is inside the Bounding Box Limits. But for some reason, the moment I increase its height a little, the prize suddenly goes up extremely fast.
For example
https://www.shapeways.com/model/1143416/rikipeke02.html

Both models are the same, the only difference is one little stick and suddenly the price is over 70€ more. Why does this happen? Is there a Bounding Box Limit that increases the price?

Maybe it's down to this:

What are the actual prices of your 2 models?
Which material?

Also go to the Model in Edit Mode and check out the Oriented Bounding Box data - this is what is used in the calcs.

The first model costs
101,06 € (132$) in white strong flexible

Oriented Bounds (used for determining printability)
In:   13.6 w x 6.5 d x 0.4 h
Cm:   34.5 w x 16.4 d x 1.1 h
Vol: 133.02 cm³




The second model costs
174,7 € (227$) in white strong flexible

Oriented Bounds (used for determining printability)
In:   13.6 w x 6.5 d x 1.4 h
Cm:   34.5 w x 16.4 d x 3.5 h
Vol: 133.06 cm³

The spike makes your models print density lower than 10% therefore you don't get the discount.

Indeed.
Thanks.