WELL, sort of. The zone numbers come from a system that predates the “sweet spot” concept:
By the time Frank Overton started talking about sweet spot, the zone numbers were already well established. Sweet Spot is the overlap between what you’ll usually see referenced as zones 3 and 4, tempo and threshold:
It makes a wild guess. Seriously, you should do the actual 20- or 8-minute protocol (or go full Kolie Moore), under conditions that you can reproduce consistently, if you want an assessment that will actually track your progress and give you accurate training zones. Or don’t worry about the number and go by feel. Riding hard for eight or twenty minutes is not an FTP test.