Remembering Decktet Card Distribution
I don't think there is any particular logic to the suit distribution in the Decktet. A quick search of BoardGameGeek didn't turn up any comments by P.D. Magnus (the designer of the Decktet, who is active in their forums) on the distribution either. I haven't been able to commit the distribution to memory, but if you want to, this is what you would need to memorize:





These are taken from the Decktet Charts and tables pdf available here.

Another useful view of which combinations of suits are most prevelent:



This is an image by HenryBlatbugIII from BoardGameGeek.