Hi Thomas, what are you trying to accomplish by doing so?
Roughly speaking 40-55% is for recovery and anywhere within that should be fine. It should be easy and allow you to recover from the prior effort. Once you go above that, you are now into aerobic work territory (i.e. some work required reducing your ability to perform the next interval).
The obvious next question would be is: if the work intervals are so easy such that you need to increase the rest interval, is your FTP set correctly?
Note: If you know you have your FTP set correctly, but still have gas in the tank after the workouts, perhaps you are coming into TR with a higher fitness level than the plan you selected calls for and should choose either a higher volume plan OR select the harder version of certain workouts (i.e. the +1, +2 variations).