Time Duration on Power Based Workout

When building power-based workouts with distance durations (e.g. 8km 95%), the auto-calculated time for the workout at that intensity is longer than what I would get by applying that power % to my pace zones based on LT pace, and multiplying that pace (in seconds per km) by the km distance. This causes my planned training load to be always higher than what I get after finishing the workout (because the system is calculating more time at the same power intensity). I’ve tried increasing my threshold pace to unrealistic values, and this does help a bit, but don’t think it’s an optimal solution.

How is the system calculating these time durations from power/distance planned workouts? Is there a way to adjust so my planned load hovers around my real load after workout execution?

Thank you.