good answer big-foot. Yes size plays into the formula, unfortunately. Also remember gold comes not only in infinate sizes and shapes, but also purity and alloys: 10k, 14k, 18k, 20k, 24k, etc....
And the analogy of the TID that an entire aluminum can gives, versus just a snippet or the tab of a can, is a good example. Each gives a different TID. Yet in each case the metal is exactly the same: Aluminum. The only thing that changed, is the size. Hence same logic for gold.