As a young entrepreneur living in Hawaii, I made and sold leis. They were primarily single plumeria leis, but I also made doubles, with plumerias, orchids, carnations, etc. The neck leis were usually around 40" long strung on dental floss. Homemade leis (like some in the photo)may be a little shorter if fewer flowers were available to make them. Most people just bought them ready made down at the airport or dock from vendors. The leis were usually worn in multiples. They would be worn like a long necklace and leave a rounded v shape opening below the neck and hang usually to mid/upper abdomen depending on the height of the person. For them to cover up to the neck they would have to be worn backwards with the long part hanging down the back. That would be extremely uncomfortable and pull on the neck below the chin. Even a large amount of leis should leave a space open below the neck. Shorter leis were made for wrists and headbands but would not fit over a head. In the above photo you can see two people in the background and the back of their leis.