This is definitely a mystery! 15 years in hobby I've had many different reef setup from small to large and all had at least 1 or 2 BTA or RBTA in my tanks. Many were bubble and very few were stringy. I'm no marine biologist but my guess the reason the bubble tip anemone is stringy is because of lighting, flow or space! I'm not saying something is wrong with your lighting or your setup! But the anemone is like reaching, perhaps the anemone isn't happy or stressing IMO. Clownfish are always good because I believe they stimulate the anemone. The feeding can be a factor. At the beginning a fed my anemones, and one day I quit feeding them because the more I fed my tank my nitrate started to rise. No matter how much fish I had in my tank I fed my tank once a day. All that food is not eaten, and your fish will find food to eat. Regarding your anemones, if your clownfish are hosting the anemone they will take care of it. FYI that is a beautiful and healthy nem.
