Believe I heard it in the WKO webinar featuring Coggan introducing iLevels, its on YouTube.
Also in a TP article by Coggan:
“Based on the logic behind the original approach, levels 1-4 remain anchored to FTP, with the addition of a new level 4a (SweetSpot) at 88-94 percent of FTP to satisfy the requests of numerous coaches who have found value in prescribing workouts at this intensity.”
And a pic showing classic levels vs iLevel
