Ideal Adobe / Mud brick wall width for heat retention (High-Sun, Low Night temp areas)

I'm wondering what the best thickness for adobe / mud brick walls when there is a lot of Sun and cold nights.

I would imagine if it's too thick, some heat may not make it all the way in, and if it's too thin the heat retention wouldn't be maximized.

In particular, I'm looking at the high Andes in Peru (Cusco region) where many houses are mud brick. They seem to have a standardized brick size and shape here, so perhaps this already has been figured out over the course of hundreds of years.

I've also been learning about Earthships, and was surprised that the thick tire walls seemed to not be too thick to be inefficient (though I don't know if they are or aren't efficient).  

It would be really nice if there was some sort of reference to use some solar datapoint along with temperature data to make an ideal wall width for a particular region. Or maybe I'm just overthinking this ha ha. Looking forward to hearing your input / experience.

Research in Australia about 'mud bricks', there is plenty of data.
In my experience 10 inches, 250mm is a minimum.
In Australia we would also encourage wide verandas around, to shade but also protect the walls from rain.

Unless you want to carry out maintenance from time to time.
Adobe, mud brick, compressed earth blocks all require maintenance over time.

I'd tend to go with whatever the vernacular architecture uses, but it's possible that with adobe the brick size may be more a function of what a person can lift, and a size that doesn't take too long to dry and won't fall apart when lifted holding the ends, rather than the optimum thickness for thermal efficiency. Cob walls tend to be built far thicker than mud brick, also probably partly due to the practicalities of construction rather than thermal considerations.  The ideal thickness may be somewhere in between.

I just found this interesting study based on 50-55cm thick rammed earth walls in Portugal. https://core.ac.uk/download/pdf/62461075.pdf