Thank you for an excellent post. Very informative. Can you please point me towards resources (url's) that will go into more depth on this subject. You have really whetted my appetite for more info.
Interesting question. I've been making soap for 9 or 10 years and gathered snippets of information here and there. There's actually no specific place I can think of that has more info than this board, but I'm always searching for more bits and pieces. The last big thing I learned came from a 100 year old patent. My sources have been all over.
A lot comes from experience. Soapcalc has been around for a long time and led me astray like it does most people. I can thank it for helping inspire some underwhelming batches. I spent a year working almost every day to figure out some of the practical relationships between fatty acids and soap.
I helped prepare a book for publication called Scientific Soapmaking by Kevin Dunn. It has a lot of technical info, some of which might be interesting to you and some not, but I recommend going through it and having it on your shelf. However, it doesn't really focus too much on recipe formulation.