When you look at old Indian photos, low brace height on a short bow usually meant low string tension as well.
Plains Indians didn't care if the feathers made contact with the bow, especially in the North, but most fletchings on Indian arrows were shorter than the brace height.
"Proper" brace height is determined by the specific tradition you are following. There are several traditions, so you must decide which one you wish to follow before building your bow.