The goal of sweet spot 4 is to increase your power output, not your CTL.
Do not, I repeat do not add more times to the rides (unless you don’t want to increase your power** 
Fresher is faster is the name of the game. I think training plan athletes @heath.meyer and @Bret_Smith can attest to how much their power went up from simply FtFP’ing.
** if you do want to increase your CTL sweet spots 1 -3 are our goto’s.