Simply put, sweet spot is where many see biggest jump in ftp as Coach Chad mentioned here:
and Nate’s big jump in ftp was a result of spending a very long time doing sweet spot work (more than 6 months, less than a year?).
My biggest gains prior to TR were a result of increasing sweet spot efforts out to 50 minutes, like stated in first post. And I believe @Captain_Doughnutman is doing similar long sweet spot efforts during his “2nd base after build” (rebuild).
Apologies if this was all covered earlier in the thread.