lastzeroThe way it's shown in the picture is not really correct. The cover flap has some extra material at the top where you can slide one of the legs of your tripod into it. The bag also comes with a rubber strap to keep the legs closed once it is in place. It would actually be sitting at the top of the bag if done correctly, not as shown on the side of the bag.
lastzeroIt's more of a question of how the tripod's weight distribution along where one of the legs would slip into the bag. Basically, one leg goes in, and comes out the other side, and boom. It just sorta, hangs there.
If you are worried about it being unbalanced I would suggest slipping a piece of cloth close to 2ft in length around one leg, and seeing how that suits your tastes as it's basically the exact same concept. The bag will just be "a bit" sturdier.
lastzeroWhat @Dinner4tuba said. A very long tripod might be unbalanced, the best I've found was ones that are the length of the bags flap, when closed.
If you are worried about it being unbalanced I would suggest slipping a piece of cloth close to 2ft in length around one leg, and seeing how that suits your tastes as it's basically the exact same concept. The bag will just be "a bit" sturdier.