Over the course of a single workout or even a week or two, many athletes can handle training 5% harder than they should. Over a training block or macrocycle, an athlete intending to train sub-threshold and threshold efforts based on an FTP that is 5% too high is very likely to burnout, see workout compliance drop substantially, and see their progress stop entirely, and they need to back way off and recover.
That’s what we’re talking about here: it’s a 5% difference in this athlete’s FTP setting. That is significant over the course of a training block. Training below threshold is not wasting time. There is a benefit, but also a cost, to all of the training we do. Success is found in balancing the benefit of your training with paying the physiological cost. If I prescribe a 3x20 at 90%, and the athlete decides, I’ll do 3x20 at 95%, those workouts will have different physiological costs (many won’t be able to do the 3x20 at 95% anyway), and the athlete will likely wonder why they can’t turn around and do their next hard workout as prescribed. It’s because the recovery required from those two workouts is different.
Now imagine doing that on every single workout you do. Personally, I would always err on the side of setting a training FTP value lower. And in this case, the athlete wants to set his FTP with data that’s based on a specific protocol when he didn’t actually execute a key part of that protocol. If this athlete had a ramp test of 206 and a properly executed, indoor (assuming this is his primary training mode) 20-minute test including the 5-min blowout effort prior to the 20-min effort, and he got 216, I’d tell him to set it to 216. But that’s not what we’re dealing with here.