Odds off the boxes - event Shugo Kingdom Adventure

This post is addressed to GMs. I'd like to know what are the drop probabilities of each one of the event boxes.

For example: what is the drop percentage of "Nether Dragon King's Sealed Box" if I open a small box (1 key) or a big one (3 keys)?.

I'd also like to know if these probabilities increase if I use a "Empress' Gold Tag - Emperor Tillirun's Treasury" or not.

Personally, I think it's bad that we don't know these probabilities. Mathematically it might be more worthwhile to open 3 small boxes instead of one big box.

Thanks in advance for your attention.