What makes a MacBook much thicker or thinner?

Apple's official website says the height of a MacBook could be from "0.35 to 1.31 cm". This is a wide range, more than double thickness.

I'm buying a new customized MacBook. When is it 0.35 cm thick and when is it 1.31 cm, for example when increasing storage or changing CPU?


The case is tapered.

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It's thicker at the back than the front.

Pic from Apple Store - Macbook