The PMP exam is one of those things that causes a lot of undue stress for a lot of people simply because they don’t know how to handle themselves while they’re in the exam room. People who do the exam online also have stress-related problems which prevent them from doing their absolute best.
If you want to do better in the “offline” exam, one of the best things for you do to is to make sure that you spend a lot of time prior sitting through practice four hour exams. These exams will help you get a feel for how much effort you have to put into staying focused.
If you want to perform better in the online exam you have to make sure that you don’t get distracted and get called away or start surfing other sites. Every second counts, regardless of whether you’re doing the exam online or offline.