The chain mustn't flop about, or it will fall off when it thrashes about under load.
I can't find the adjusting bolt you mentioned in the picture. Such things are usually designed to be accessed with a socket spanner, often with an extension shaft so that the torque is applied far away in a spacious region. I can see one smallish bolt running laterally on the right side of the picture, and it looks to me as if it can be accessed with a socket and perhaps a short extension.
Mechanics are not fond of barked knuckles, and engineers are usually trying to design things that mechanics will cope with successfully. Any time the job involves lousy access and skinned knuckles, it's time to replace the design engineer. Can you post a picture that shows the bolt and its environment?
