I don't mind the question but I really don't know the answer. You are right that for me fragrance is the biggest reason I had problems and today I will abandon a fragrance in goatmilk if I have any issues. I don't think I know how to determine that tipping point of too hot. However I am in better control if the soap heats up slowly rather than fast and I can control that by keeping airflow around the mold which I think keeps the soap from getting as hot but slows down how fast it heats up which makes it easier for me to stop the overheating if I put in the freezer.
I have not heard many soapmakers complain of the speckly center and wondered if it was my formulation that caused it when overheating. I use about 60% hard oils (coconut, palm kernel, palm, cocoa butter, shea butter) 40% soft oils. I soap with oils abt 95-100 and lye/milk about 80-85. I like the 95-100 temp because with 60% hard oils it helps keep a more fluid batter and prevents the thickening of false trace. I use lye/milk solution at 33% and use 100% frozen GM for the liquid. I unmold at 18-24 hrs and cut two days later. My batch is about 42 oz and I am using a wooden log mold with a mylar liner.
Today I always I rest my molds on a "shelf" of 2 lids where the molds are supported at the ends and there is about 1/2 inch of air flow beneath the log. That really helps in keeping the log a little cooler and causing them to heat up slower. I don't cover the soap. I let my hand judge the heat of the mold. If I touch my hand to the wood mold and it is very warm to hot within 15-20 minutes of making I do put in the freezer for 30 min to an hour. If the mold is slightly warm at 20 minutes I don't put in the freezer at all. (My wooden log molds have mylar liners rather than silicone. I use mylar because that's what I did for my not quite standard mold size 16 years ago. I do think silicone might insulate better which might make it harder to judge the batter temp based on the feel of the heat of the wooden mold.)
I tend to use only fruity, herbal, and earthy scents in goatmilk; BRV, OMH, Lavender sage, or my patchouli/lavender/sandalwood blend never go in the freezer at all. If I do put a log in the freezer I also make sure there is still airflow all around, either by it being on a wire rack or using my lid shelf. Even in the freezer I think the soap builds up more heat in the center when setting directly on a solid surface.
Sometimes when I unmold the log it can look like a partial gel at the corners but within one or two days it doesn't. I have always thought they were still completing saponification. I will say that I have only had partial gel in soaps when using mint essential oils and that in the corners; so avoiding partial gel has never been something I have ever had to deal with much as a soapmaker in water or milk. I assumed that the temps I used or the formulations or the wooden log molds prevented the problem. My goat milk soaps are not getting so hot that I can clearly see the jelly like clearness at the surface. So I could be clueless and they might not be gelling. I think they are but what I really know is that my milk soaps now are not getting quite as hot, the center is not substantially hotter than the edges, they are heating up slower but may be staying warm (but not hot) longer. I definitely don't have partial gel or an ugly center.
Why not try one without the freezer from an easy fragrance you know doesn't overheat like Black Raspberry Vanilla. You might be pleasantly surprised.
... I was thinking about it all wrong! I get it now!
