Sorry, but I'm not sure what you are referring to when you say banquet. Can you post a picture?

eagledzines, a banquette is like a built in booth for seating (see below for examples of both built in and free standing ones, with different chair heights). I assume your question, jadams, is about the height of the back of the banquette. I don't think it has to match the chairs, but lots depends on context. Many banquettes are set in windows, so they don't have the option to be as tall as chair backs. What's important is that the seats are all the same height.

Thanks feeny. Your comments about the seat height is really the key.

The distance between the seat ht and table ht should be 12"

Thanks fenny. That's very helpful. Yes, I was referring to the height of the back of the chairs and the back of the banquette. Ours is not set in a window so we have some flexibility. I will double check seat heights. Good to know.