If it's Zwift supported, it should work properly when set up properly, right?. Have you tried it with trainer in the Road setting? Are you having to lower your actual weight to get your in-game speed where you think it should be? Is that expected speed based on what your Bolt is displaying, or your actual road experience? I ask because I wonder if there's a possibility you're actually producing lower wattage than what you think, like maybe your pedalling speed is high if you're in the small chainring, but power level is actually low. Did you try riding in the large chainring? Any difference?

Also, I'd expect Zwift's virtual power curve to be more accurate than Powercal, but it could be interesting to compare. Could you connect Bolt to Powercal and leave the trainer connected to Zwift just to have two power recordings of the same ride? That'd be ideal, maybe.