Hi Christian! I wonder if you’re seeing cold or hot process shave soap recipes made with just sodium hydroxide? That would be normal to have a lower amount of water.
For dual lye soaps – you need extra because of the potassium hydroxide, but also because dual lye shave formulas have a really high amount of stearic acid. The extra water gives you plenty of time to work with the soap.
If you check the example recipes I link to in this article, they all have at least 5x the amount of water than lye (one has about 7x!)
I don’t know if it’s a hard and fast rule though, but more like a recommended practice. The great thing about soapmaking is that there’s plenty of room to experiment and do things differently if you’d like! ?