How do the underground statues actually work?

So I have done quite a bit underground and have gotten quite a few regular and shiny statues. However, I am unsure how exactly they work.

From what I have seen from my googling, regular statues increase the spawn rate of Pokémon of the same type as the statue, whereas shiny statues make it possible for that specific Pokémon to spawn. However, a lot of the sources I have found seem to have conflicting information. I have also been unable to get a shiny statue Pokémon (eg. Rotom) to spawn and am still not quite sure if my understanding of the regular statues work.

So overall;

• Is my understanding of regular statues correct?
• Do multiple types of regular statues work at the same time (ie. can I make Dragon and Fairy spawn more often at the same time)?
• Do Shiny statues work with regular statues at the same time?
• Do multiple shiny statues of different pokemon work at the same time?
• How do shiny statues actually work?

If you have any specific values of spawn rate increases, that would be great as well!

According to Serebii, the only thing the statues do is add points towards different thresholds for boosting a specific type's odds of appearing in the rooms.

I have not seen any reliable information about the shiny statues allowing different pokemon to spawn, and based on several hours in the underground I have not seen any evidence that the statues will change what pokemon are available.

The boost is only for one type, so the one you have the most points in will be the one that gets boosted.

Shiny statues are the same as regular statues, but the points they contribute are doubled.

I have just verified that duplicate statues contribute points to the total as well.