Hi,I would say the best way and fairest way to do it would be to calculate the cost of 1 small book as you say in your example through to larger books and your biggest, heavier book. Then calculate an average price for your postage. Okay so it may cost you on some orders but you're gaining on other orders so it will even itself out. That's the best way to do it and the way most people already do it. Hope this helps,