[Raise]

For example, I have 2 bluray movies that are both 2.35:1 aspect ratios, but one has bigger black bars than the other. What else besides the ratio is causing the difference?

 

[Stew4msu]

What are the movies?

 

[CAVX]

Just because a film is credited as 2.35:1 on the case does not mean that is the true AR of the film. If a film is really 2.40:1, then you will see more slighty black bars than a film that is 2.35:1.