I personally don’t drop my FTP at all and start every interval that isn’t super high on the TT bars. Leaving the bars is a bail out for when things get too hard, but over time the time to bail becomes longer and longer, particularly at FTP to +10% or so.
In the off season, like now, I have a lower threshold for bailing. By spring it is everything but hard sprints.
I guess I could start off with a lower FTP and move towards it but it just happens anyway that the two positions become very close at even up to VO2 max.