I really do believe that chicks need to see us humans in context in order to accept us as non-threatening. I have had a succession of side access brooders after the totally un-successful box-on-on-the-floor-reach-down-from-above brooder. The most successful of my indoor brooders was a plant grow-window where the chicks could observe life going on all around them. Those chicks I thought at the time were the most fearless I've ever raised.
That is until I began brooding outdoors in my run. My chicks are the size of large bugs, and are completely fearless even when I and my huge feet am stomping around in their pen. They are running around, curious, and if i sit down, they are on me in a heartbeat.
For my complete analysis of why this works so well to produce fearless chicks, read my article on outdoor brooding linked below my post.