I disagree with this. I don't believe you can use an oil calculation for the Coconut milk. Not when it is taking the place of water. See
this thread for more discussion on that topic. I do understand that whatever fat may be in the brand of Coconut milk one uses, there is bound to be some additional fat that may up the SF of a recipe, so in that case, if it were me, I'd simply change the SF number in my
lye calculator.
Yes, I have put cardboard box molds in the oven many times for CPOP. I set my oven at the lowest temp (about 150
° F or a bit below). I cover with either another piece of carboard or plastic wrap, then drape with a towel. Usually I turn the oven off right away, but I have on occasion left it on for a half hour or so before turning it off. It is an electric oven. Not sure I would do the same in a gas oven with a pilot light, though.
I get the same numbers as you using a 5% SF and no water discount, so I see nothing wrong with that part of it. As I said above, if it were me, I'd probably have decreased the SF from the default 5% to something like 2% because of the fats in the Coconut milk, but that would depend on what the content is on your particular brand. According to this Wikipedia article, the amount of fat in coconut milk can be 5-7% if it is 'thin' and 20-22% if it is 'thick'. It also says about half the saturated fat in coconut milk is lauric acid, which if saponified should contribute to hardness, cleansing and big fluffly lather.
Then again, since your recipe is so high in CO, maybe decreasing the SF isn't a good idea after all. That's a lot of cleansing power in your recipe, so maybe it's just fine as it is and would be fine if the milk brings it higher still.
So I have a couple of questions for you:
Did you line the box with freezer paper or, if no, what did you use for lining the box?
Has it firmed up some since by just being exposed to the air? And how long has it been sitting out?
Has it reached room temperature yet?
If it were me, I would take a temperature of the soap, heat the oven to 150 or the lowest your oven heats to, take an inside temperature of the oven (I always do this because I learned that sometimes oven temperature sensors malfunction) and CPOP the soap for the rest of the day (turning the oven off after the soap starts to heat up, if it is at a low room temperature).