Your Ideal Reader can be of tremendous help when it comes to figuring out how well you did with the back story and how much you should add or subtract on your next draft. You need to listen very carefully to the things I.R. didn’t understand, and then ask yourself if you understand them. If you do and just didn’t put those parts across, your job on the second draft is to clarify. If you don’t—if the parts of the back story your Ideal Reader queried are hazy to you, as well—then you need to think a lot more carefully about the past events that cast a light on your characters’ present behavior.