Im also new but i have noticed that when i put my kinect 360 higher up it tracked me a lot better.
With just three feet i think it will hardly have enough space to see you, im about 5feet8 and i need to be about six foot from my kinect 360, which is mounted about four feet off the floor, for it to full see me.
D4VR says it needs to see your head when calibrating, im guessing this is so it can “hang” the virtual trackers from it.
IF the trackers are at the right height when you are in the steamvr environment, ie you look down and theres one for your hip and another for each foot, at about the right height you should be fine.
In VRchat the floor height will differ with the size of your avatar, to help this ive actually made the arms on a couple of avatars shorter, closer to the length of my real arms.