As a side sleeper I had the opposite experience unfortunately, so YMMV. The Manta Pro is touted for side sleepers, but I've used both the pro and original and they both suffer from the same problem: it still slips around and the walls of the eye cups press into my eyes as I sleep. I gave it a few weeks of waking up with soreness and misaligned vision. No amount of fiddling with eye cup positions or strap tightness helped. The thickness of the strap is a fundamental design problem with the Manta approach, even with the expensive tech fabrics on the pro. It's overbuilt.

After trying about 10 other sleep masks, I ended up with the Alaska Bear Silk Two Strap [1] which has straps so thin they're imperceptible, and a much more effective retention mechanism, for a fraction of the price.

[1] https://www.amazon.com/ALASKA-Natural-Blindfold-Super-Smooth...