Actually, Marlborodog got it the closest. Anyone who has dealt in retail sale will understand better.

To keep it simple, there is a cost to mining, same as anything else, which determines what the profit is. If one can mine 32% ore and end up with a 10% profit, you have the basis of a successful business plan. If you can use the same process but mine ore that will add 6% to the final selling price, then you have increased your profit by 66%. That percentage figure varies as you go up or down the scale. If the operation is a huge success to start with and you can mine 32% ore for a 25% profit, the added 6% is less lucrative. Conversely, is you are mining 32% ore for a 3% profit, then the added 6% will result in a 200% gain. Clear as mud.

Best regards

K