A 3% lye discount for KOH is the same as a 3% lye discount for NaOH. In either case you end up with the same amount of superfat.
The purity of the alkali does affect the lye discount so if you want the most accurate results, you'd want to incorporate a correction for purity. That's not a difficult correction to make even if you have to do it by hand, unless you're really uncomfortable with math.
As defined, lye discount and superfat are not based on the water content, only on the fat and alkali. A 3% superfat in a diluted liquid soap is the same as a 3% superfat in KOH paste is the same as a 3% superfat in bar soap.
This is the basic info you wanted -- if you want the full math and chemistry background, let me know.