What are the rules of sea-monster transformation in Luca?

In Luca, the sea monsters transform whenever water touches them. However there are times they are completely transformed despite being out of the water, such as when they’re heads are sticking out of the sea, and at other times they are human despite being wet, such as when jumping out of the water without drying themselves off. And other times, they are partially transformed, such as when it is starting to rain.

Are there any consistent rules in regards to the sea-monster’s transformation to humans?