Probably three or four. What I was thinking was rather than chasing just FTP up, chase the intervals longer too.
FTP up is the only variable if sticking to stock plans. But if you start to lengthen the intervals that gives you another, very useful, dimension to play with.
If you do that and also throw in some short power build weeks you can work the whole power curve, have some extra variety and build durability too.
Hope that helps.
Mark