Yes, shipping does 'go down per copy' depending upon how many we order.
I just went to Schulzes site and ordered 15 more books (yay!) - shipping was (FedEx was cheapest) $16.43.
I went back and put one book in my cart - shipping was (Priority was cheapest) $9.24.
We've been shipping worldwide for over 10 years (before our Herbal Apothecary we were eBay Powersellers)...and this has been the case for quite a few years (particularly with UPS). The smallest/lightest package via UPS ships UPS ground (depending on 'zone') for around $8-$9 dollars...but if I order or ship over 40-50 pounds, the shipping is only $1 per pound.
Also, some people don't realize it, but USPS rates are now 'zone calculated'. It's cheaper for me to send a 3 pound package to a nearby state than it is to send the same package further away. However, the Flat-rate option is not zone-dependent.