Does It Matter Which Gear I'm In?
I'm on a smart trainer in ERG mode, does it matter what gear I'm in? The answer is yes. If you are in too high a gear, you may have trouble reaching your recovery targets during the workouts. This is especially true for wheel-on trainers but can happen with direct drive trainers also.
The opposite may also be true. If you're in too easy a gear, you may not be able to reach the higher targets.
Which Gear Should I Choose?
Each gear will have a "basement" power level. No matter what number the app is sending to the trainer, the trainer will not be able to get below this basement level. If you are in this situation, try switching to an easier gear. Keep switching until the lowest power your trainer gives you is below the lowest target the app gives you. That's the gear you need to choose for ERG mode.