Most calcs assume NaOH is 100% pure, but the actual purity is never 100%. If the actual purity is, say, 95%, then the assumption of 100% purity builds in a hidden superfat of the difference:
100 - 95 = 5% hidden superfat.
That means if you set your superfat/lye discount to 5% in soapcalc and use 95% pure NaOH, your soap actually has more like 10% real superfat. If I remember correctly, soapee.com allows you to set the purity to something other than 100% (at least you can do that for KOH), and that's a step in the right direction.
You can use a higher superfat to make a milder soap, but that's not the only way to handle this issue. I formulate my recipe to make a mild soap without needing a higher superfat to be mild on my skin. I use a 3% superfat/lye discount for pretty much all of my soaps. This 3% is going to be closer to a true 3%, since my personal calc also includes a correction for alkali purity. Everyone's preference and skin are different, so I'm not saying my way is the only way. But it is entirely practical and reasonable to formulate a soap with 2% or 3% superfat/lye discount and have a lovely, mild soap with lots of bubbles.
edit -- By using less superfat, the soap will make more bubbles for the same blend of fats, so you can actually reduce the cleansing/stripping fats -- the ones that make bubbles -- and end up with a mild bar that's still bubbly.