I would try the next size up and see. Also we try and point his willy down 😄
You can't always go by the weight chart it's more about how the baby's built. But if you're having constant leaks you should try a different brand or size. As far as overnights go they do make overnight diapers which are more absorbent and expensive but you can also just put a maxi pad in the diaper before he goes to sleep and that should help catch everything.
Try the diapers from countdown - the little ones brand. These r quite compact in fit around the waist compared to Huggies and the other brands. My son is slim and tall and I had faced a similar issue