I understand the concept, It just has a large mechanistic hole in it that's either not being explained or is being missed.Because the increase of t4 to t3 means your natural t4 pdoduction won't be able to keep up with the demand which eventually drives your t4 down. So over time the lower the t4 gets the lower the t3 will get as well as it strives to find more.
The only thing that's being said is that T4 will drop because it "Can't keep up with increased conversion", but if total thyroid output remains the same (presumably topped out and trying to 'keep up'), that newly-created T4 has to be going somewhere, right?
The only way I can see the math working is if Thyroid output decreases irrespective of any drop in fT4 from increased conversion, which is a different mechanism and argument entirely.
I suppose it's also possible that with high-doses it simply takes a *long* time for homeostasis (and a decrease in fT3) to be reached, and that's what's being seen.
I've personally never seen anything in bloodwork but a drop in fT4 and a bump in fT3 that reaches homeostasis fairly quickly. But I've also seen very little well-controlled data in the 6iu+/day range.