I’ve never used my mtb on the Kickr but I did adjust my road bike (it never leaves the trainer) so it was a closer fit to my gravel bike (super comfy) which is closer to my mtb bike fit. I swapped out the stem and adjusted the seat position. My body is more upright, and the reach is corrected. And you could also adjust your seat and shoe cleats to better mimic your mtb foot position.
Stay rigid so you better understand the numbers and can compare them to others if you want to.
M