I think the difference between those threads and what I've done was pitch a separate amount of the same yeast used (at a greater rate) just for the FFT sample rather than drawing off from the pitched carboy wort. I also fermented it at a higher temperature so the yeast would work it's way through the wort sample quickly.
I think these steps* mitigate any separate factors concerning the amount or performance of the yeast compared to the actual fermenting beer. I mean really I'm just trying to get to the limits of the wort's fermentability. The actual beer may or may not reach this limit, and could be higher since the pitch rate of the actual beer is lower.**
Truthfully, after thinking about the original topic a little more, I wonder if mashing at 152 for so long and mashing out at 165, rather than at 170, may have released more dextrins than I hoped due to the alpha amalyese being "on" for so long. (Assuming that this FFT is correct.) My efficiency was about 8% higher than I expected, so that's not really outside the realm of possibilities.
*And as a result made a really awful sour tasting sample as I learned today.
**All of this lovingly paraphrased from Kai's FFT page.