This thread has devolved into a scale argument.
The questions could easily be settled by looking at the "official" website and the wiki.
From the website www.avatarmovie.com
Na’vi vary in size, by region and genetic history. Maximum recorded height is 3.9 meters, with a mass of 290 kg, for a Na’vi male. Adult Na’vi males in the region of Australis surrounding Hell’s Gate
(where the movie takes place), average 3 meters in height
(9'10")and 210 kg. Females in this region average 2.8 meters/190 kg
(or 9'2") . Other examples of gender dimorphism are the pronounced pectoral tendons and sternal prominences in the male.
From the Avatar Wiki https://james-camerons-avatar.wikia.com/wiki/Avatar_Wiki
The indigenous Na'vi are, on average, approximately 3 meters (~ 10 feet) tall, with smooth, striped cyan-colored skin, large amber eyes, and long, sweeping tails. Their bodies are more slender than humans. They are the only known extraterrestrial species discovered to have human-like consciousness and intelligence. Although the Na'vi are hunter-gatherers with technology equivalent of Earth's Paleolithic epoch, they have developed a sophisticated culture based on a profound spiritual connection to other life on their moon, each other, and an encompassing "goddess" they call Eywa.
Also from the Wiki
During the flight, the avatar
(Human/Na'vi Hybrids)progresses from coin-sized embryo to a near adult size of
nine feet (2.75m). Gentle blue light tailored to mimic the natural Pandoran daylight spectrum aids skin formation and guarantees amniotic fluid sterility. Nutrient-rich broth is circulated through an artificial placenta, a purpose-designed matrix of spongiform blood vessels and monitoring electrodes. Engineered hormones are used to stimulate rapid growth and ensure correct organ development and muscle tone during the interstellar journey. Avatars are normally grown 'en-route' to Pandora while their operators sleep in cryo-hibernation for the journey.
Some known differences between the avatars and Na'vi are due to the influence of human DNA.
■Critically, the avatar brain and nervous system are modeled to precisely match that of its human operator while still maintaining appropriate Na'vi cellular biology. The avatar also possesses the necessary nervous system pathways required for the control interface.
■Avatars retain the human configuration of five digits on each hand and foot, rather than the native Na'vi who possess four digits on each limb.
■Avatars possess eyebrows, while the Na'vi are hairless apart from their scalp and a small tuff of hair on the tips of their tails.
■Avatars display slightly more human-like body musculature and structure than the Na'vi (this is especially apparent when comparing the build of Jake Sully to that of the male Na'vi of the Omaticaya clan; Jake's body structure is sturdier than those of the more willowy Na'vi).
■The Na'vi have large lemur-like eyes, while the eyes of an avatar are usually smaller and more human-like.
■The Na'vi nose is flat and cat-like, while the nose of the avatar has a more human-like pronounced central ridge.
■The queue of an avatar starts at the base of the skull, whereas a Na'vi queue starts at the top of the skull. The reason for this is not clear.
So bottom line is that HT got the scale pretty much right.