How long have they been in the tank? I found my Flame Angel took a good 1.5 - 2 months of getting accustomed to me before it wouldn't hide all the time. Other fish seem to be ok with a person right away.
I think it also depends on how quickly you approach the tank. Sometimes mine still get spooked if I walk by quickly.
You might be able to lure them with a little bit of food when you walk up all the time too
Mine seem to know when it's time to get fed.