Your TrainNow workouts will tell you the TSS before you do the ride. So, for example, if you see a ride in TN and it says “Achievable”, 60 minutes, 60 TSS, then just use the filters and alternate workout to pick one that says “Stretch” or “Challenging” with more TSS through higher IF, or choose one that is longer and therefore generates more TSS.
Also, are you using the same power meter indoors and out?