Mine do the dash anytime people approach, I am use to that. I will try find a couple blankets and give that a go. However my house is very quite during the week, no kids at home, just me studying during the day and night sitting on the couch not really moving much at all. So I find it hard to believe that it would be external influences causing them to stay low. But I will give it a go, just so I can rule it out.
I also wonder if there is too many fish in the tank and to many hiding holes/rock work etc and not enough open water, causing the fronts to get the hebe gebes and making them stay low and at the back. This of course is a difficult one to counter with the T's lele's calvus and the such.