What's the best length for ear savers for PPE?

For those of you who are getting feedback from first responders and health care workers who wear masks all day, what is a good length for “ear savers” - you know, the sewn or crocheted or knitted strips with buttons sewn on to hold the mask away from the person’s ears to make them more comfortable?

I’ve made them in several sizes, but don’t know what is the most needed size.