I'm exclusively a side sleeper. You use a U pillow, which the X5A rests between (something akin to the neck pillow you typically see used for airport travel; there are a lot of variations to test to find whatever works best for a given person in terms of comfort). There are also a lot of variations of cut-out pillow options for headphones/earbuds and ears (people with sensitive ears), for side sleepers.
So: X5A hard plastic ear segments between U shaped pillow (the U shape supports your skull, the hard plastic goes between the U) -> then ideally something very soft under the U shaped pillow which buffers between the hard plastic of the X5A and your mattress, so the plastic never fully presses against anything firm (if the plastic of the X5A meets something firm, then your skull is meeting something firm). Very soft memory foam can work great for that, or really anything super soft.
Does it cancel human voices effectively? I have tried a few such earphones but none of them is good against human voices. I'm particularly sensitive to human voices.
With earbuds it'll easily wipe out human voices, including louder voices. A number of years ago I rented an apartment where the walls were paper thin. I experimented with the most comfortable noise to utilize via the earbuds (which are worn inside the X5A). Either music or brown noise would entirely eliminate 100% of routine neighbor noise combined with the X5A headset. The brown noise was hyper effective in tandem with the X5A and far more comfortable compared to white noise (which is almost always a mistake to use as a noise interruption agent).
X5A + brown noise = you can't hear alarms, you can't hear dogs barking nearby, you can't hear yelling. All normal noises vanish. So be aware of your surroundings, you won't hear a typical fire alarm either for example.
The 3M X3A + brown noise will drown out bird chirping and ~95% of human voice noise. The X3A is far more comfortable - slimmer - than the X5A. If you need max reduction of neighbor annoyance, nothing beats the X5A though. Neither of these are particularly expensive, they're both worth trying.
Some people try to use headphone type noise cancellation, which is mediocre at cancelling most noise. I found instead of using headphone noise cancellation, it was far better in most circumstances to use the X3A + earbuds while working - that tandem was very comfortable to wear for long periods of time. The X5A is not very comfortable, it's just max effective.
