Big difference between sustained average power between climbing vs flat? Is this a function of my conditioning and training? What can I do to help improve this gap?

Hello,

I recently gave Zwift a try this winter and noticed that there is a big difference between my sustained average power when climbing vs riding a flat at my threshold heart rate. Basically I find I can sustain a higher power when climbing at the same heart rate.

To give you an example, on Alp de Zwift I am able to maintain about 277w on average for the entire climb (58mins) whereas when I try the pace partner or do an hour ride on the desert flats, I find I am only able to maintain an average of about 240w at the same effort/HR. Where I live, I never really had the opportunity to have a sustained hour long climb and though I understand that Zwift is only simulated and not real, I'm a bit surprised between my ability in the different scenarios.

I was wondering, is this a function of my previous training and conditioning? Is this normal? In the past, I usually focused on sprinting, intervals and short high intensity group rides. Has anyone else experienced this?

Thanks in advance!