Like you, mine have no problem sleeping or napping, they will do it themselves, because I too have been praising them alot.
But it seems to have little to no effect on their energy bar.
Really? Because that's not the case here, they will fall asleep in bed exhausted, wake up still tired (takes a min for the bar to register the increase) then go for a nap. By the time they wake up from the nap they are at about half full for an energy bar.