IMO, it is the respectful attitude or lack thereof from the COS next to me that makes the diff.

On a FRA-DXB in Y I failed to sleep b/c pax kept whacking me with her arms and jangly bracelets, rudely kicking her overly large hand luggage into my legs and under my seat, and ignoring my requests to please stop laying her things across my knees as she pulled them out of her bag. "Don't touch me" would have been my next request.

Yet on a SFO-NRT in Y, pax in seat next to me read his book, did some work, and respectfully avoided my person best he could when I was sleeping by folding his arms and carefully moving about. I appreciated this so much I didn't mind at all if he put one leg on either side the seats and had the armrest up.

Both were seat extender COS, but even if they had been Little People my opinions of them would have been the same.