Either 1 or 2 percent is fine — or even 0.5 percent, or 1.5 percent, or numbers in between! It's up to you and how things work with your recipe, your typical water, and your environment. I don't use more than 1 percent or 1.5 percent, because citrate crystals tend to form with my usual recipes and very humid weather when I use more than that. And I don't like them, at all. The bars also seem more drying, but that might be just my imagination.
Ha ha, I'm really not the person to be talking about math and should shut up right this minute
but yes, using
2 percent of your oil weight means
45.36 grams of citric acid, but that works out to
28.3 grams of extra lye to maintain the same superfat (45.36 x 6.24 = 283 then 283 / 10 = 28.3)*. Rounding the numbers for easier measuring should be okay here. Good luck!
*And if I'm doing this wrong, someone please, please, please correct me!