I have been reading some posts by Marco, from 2005. Interestingly it seems that in Italy, perhaps today but at least in past times, water was the ingredient that derived the amount of salt, yeast and flour. Unlike what we are used to, being flour.
At any rate, Marco was describing in one of those posts that for 1 litre of water it is common to use 45-55 grams of sea salt. This results in 4.5%- 5.5% salt, not % of flour however.
Since it seems the flour amount is based on texture of the dough and other factors including humidity and age of the flour, I wonder how % of salt using bakers % would equate with the 4.5-5.5% of the water?