Training peaks %threshold workout but pace planned not the same in zwift?

[Ian_G_PPF (Ian)]

i had a training peaks workout that called for 115% of threshold pace. that would be 8:42 / mile. but in the workout in zwift it wanted me to run 7.7 mph for those intervals… a pace of 7:48 / mile.
what is causing that discrepancy and how can i fix it?

thanks