Yep, anywhere is fine. If you use two or more, it is good to spread them out. Depending upon how good the seal is, once equilibrium is met, the entire space should be the same. If you have leaks in your storage unit, then the areas near the leakage, may be slightly more or less than the area directly near the packs with a gradient between. The larger the space, the more this becomes a reality. This is all theory, though. In real life, likely doesn't make much significant difference, unless it is a big leak or a large volume.