When someone says that you need more than one lockon to the layout, they should say that you may need more than one attachment point or you'll get power dropping issues as the engine gets too far away from the single lockon. There are reasons for this such as power loss from the track connectors, voltage drop from the track itself not being a perfect conductor, etc.
Ray knows much more than I do, I'm just confused on how you're going about this. Adding packs (power source) sounds wrong to me, unless you're dividing the sections of the layout into blocks?