I have different experience with my Hengeli, they are hardy and school very closely, closer than my neon tetras.
They sometimes group and corner in my 10g, where the water current is strong.their swimming are a bit erratic, maybe "crazy" is a more suitable word. At first I thought it was my water parameter/co2 issue; but they have been doing this for more than a week and they seem enjoying this. Its funny to see them exercise against strong current, then blown away, then do it over and over again. They do this when I add water during change too, I think its their nature loving current.
They other story about their toughness which i dont want to share is, when they were still in acclimation jar, I dropped a rock 2x its size onto one of them, instant knock off; 30 sec later, it struggle to swim again, but up-side down; 2 mins later, it swim normally again!