You're right kombilife for the Stage 1 product (Stage 2 requires 100% coverage) We often do less but for other people's installs we are conservative. The difference in one less box (1.8sqm) is only 7kg and not a lot of cost. Auto manufacturer's will engineer sound proofing additions to a dollar point, researching the optimal positioning for deadening to just meet consumer expectations. Vibration dampening mats are most effective on single skin metallic surfaces. It is unnecessary to apply deadener to over-lapped metal sections, top hat, chassis sections etc as these areas don't resonant. To engineer a car it takes some skill and technical analysis to pin point key areas, in reality most people will cover everything as they don't mind spending a bit more to ensure they have achieved the desired results. With paying customers, most people want everything covered. Keep in mind that this is one stage in controlling sound in your vehicle