Just a thought; is there a way add an extra interval at the end of a work out - in the same way you can extend warmup or cool down?
I know you can choose a +1 workout or increase intensity during a workout but sometimes you feel great (maybe I am getting fitter…hmm) at the end of a workout and feel like you can do another interval.
The other day I was unmotivated - after a few really hot days in Sydney. I choose the shorter workout. Struggled through the first few intervals. Halfway through the last interval, the tiredness left and felt fresh and strong, but it was the last interval.
Just a thought.