I just noticed FrostyTech has a
very unique test platform. They basically just apply heat to the heatsink; no enclosure, no other fans or components messing with things. They haven't reviewed the FX100 either, but they did make an important observation about the orientation of the heatsink fins with fanless cooling. When
comparing the CR-95C and the Silverstone HE02, they found the CR-95C was uneffected by orientation, but the HE02 went up 12C (!) when moved from a tower to desktop/cube orientation.
Looking at the fin orientation of the FX100, I'd be willing to bet it would be somewhat effected, but in the opposite way of the HE02.