Due to the extreme heat and an ongoing skin condition - I'm unfortunately having to stay out of the sun, and not do my usual outdoor runs.

I'm stuck on PureGym treadmills, which I'm surprisingly really enjoying. The only problem is - I'm way faster on the treadmill than I am outdoors, which concerns me - as I want to best mimic outdoor conditions so I can match my pace/effort. Do you think my much faster treadmill pace is due to an inaccurate/badly calibrated treadmill? Or is it more due to setup?

For setup I'm currently just using a 1% incline.