you asked: Chef has some beans and some jars. How many beans should fit in each jar if he minimizes the airspace between them?
unless you work for codechef, you should elaborate with all the details that you know. What is in the files? Did you write the compression or use stock? If its stock, what options did you check? Did you check your % compression computation for a bug (are the actual written files all the same size?)? Did you check that you used the different algorithms (copy paste type error?). Etc. No code, no details about the files, ... it can't be answered like this.