Today I was reducing some FASW at 100°C under a cupboard to make it more concentrated. I left it for 10 minutes and when I came back, the the underside of the cupboard had yellow sticky spots and it smelled like DMT fumarate.

So, it's pretty safe to say that reducing FASW results in loss of DMT as I'm sure the same thing happens at lower temperatures, it's just that the process is slower and less noticable.

If this is true, then fumaric acid used for acid boil in an A/B tek would also reduce yield.

Solution: make a concentrated FASW by dissolving fumaric acid in boiling water, then there's no need to reduce it before proceeding with water precipation. Don't use fumaric acid when doing A/B acid boils.

I don't claim to have discovered something new but I hope it helps!

Smelling the sticky yellow spots is how you deduced all that? Hm. Lol. You might want to look into what it actually is that's yellow and sticky because I don't see it vaporizing out with the water. But it is possible I suppose. Did you see any loss in your final product?