First of I want to make sure you don't misunderstand, this is not an issue, I am merely curious about why the sizes have been chosen to be multiples of six.

It seems highly more logical to have props in multiples of two, since you could create any size with the right combination of binary props (powers of two), as opposed to SProps multiples of six.

I fail to understand why the author has decided to use multiples of six. Shadowscion, would you please allow us to understand your choice?