You mix several different things here.
My appologies if I mixed up different things or didn't explain it well. I'll try to explain it better :)
I agree that smaller volume needs less energy to heat and I also agree on the insulation part, but again the surrounding climate here is the main factor, as you pointed out. Maybe in other coastal parts of the world it's a different story, but here all the houses are built the same way and for a reason - > high humidity all year long, 9 months of almost constant rain and strong winds. You won't see a native here with an umbrella, because it's pointless to have them, the wind tears everything down :)
If something is insulated well enough you keep outside humidity out, too.
Our houses have walls that are usually around 30cm thick (different layers) + styrofoam (like in this picture
). I think this is a good insulation. I've been in many other houses and everybody has the same problem with the mold and the humidity no matter the insulation. I've also been to a house that had scrap pieces of paper in the insualtion and it's still the same problem.
Plus the human body also releases a lot of fumes just by breathing, not to mention the fart-festival after some good beans :) Cooking also produced a lot of fumes and humidity.
It needs to get aired often that's the only solution and afterwards you need to heat it often as well.
"Many micro-houses have one large sun facing window and lots of smaller ones...
Maybe that's the key here. From Semptember until May it's raining almost every day here. During that time it's also quite cloudy, so not much sun here. We also have 2 very common kinds of wind, "jugo"
which keeps everything warm and moist and [url=https://en.wikipedia.org/wiki/Bora_(wind)]"bura"[/url] which is cold and dry, but either one of them is very strong and usually comes paired with the rain so humidity assured.
Every house is build so that the most windwos are facing East, that's also where the house is facing, and the other sides of the house either don't have any windows or have only a couple of them.
Hopefully I explained it a little bit better this time. I do like these microhouses, it's just that they aren't perfect for every place. Especially with a climate like it is in Dalmatia :)