Why can I put out out 100 watts more on descents than on the flat?

Is it normal that I am consistently able to hit 100 hits higher at max effort on descents than on flat or uphill?

Can you post a run down of your setup.

Sure, though I don’t think it’s an issue with Zwift per se. I have a TacX iFlow smart trainer with an aluminum road bike with Sora components.