That chain is perfect and the opener could be lower but its just that whoever installed the door never put a strut to reinforce the door so that is pretty much what the problem is here.
The arm should be longer, and the opener should be lower. The arm should be angled between the 1 and 2 o'clock position and the opener should be mounted 2" above the highest point of travel (when the top section folds up) and the motor height should be set with a 2x4 on the door with the rail resting on it. you'll also need to reinforce the top section. I hope that helps, and good luck.
Your top section needs a reinforcement strut and that should fix the issue for the time being, however eventually you will need to have the section replaced..