No bars is a good thing. You may prefer to see them for whatever reason, but other than maybe a center bar I wouldn't want to see them!! Your fish clearly are doing well, I'd keep doing what you are doing. Just took this photo of one of mine yesterday. You can clearly see his bars are lurking there but he doesn't have them turned on (or inverted) which is a good indication to me that its doing well. I want to see this, dark bars makes me double take at the tank to see whats wrong.
Same with this one. Center bar showing fairly well but the others are quite hidden, this is a good sign IMO. I'm ok with the center bar but anything else again I'm double taking at the tank.