Some people are misunderstanding what you're asking and some don't have experience with getting a shed delivered. As I've moved I've gotten sheds made and delivered and it sounds like what you are being told is what I was told as well.

I've done 3-4in stone as instructed and bordered with pressure treated. I've even used stacked pressure treated 4x4s as a retaining wall with large metal stakes going down through. That shed is 10 years old and the wood and shed are in new condition. It also helps that the siding is vinyl and not wood.

My latest shed was 12x20ft and the way they deliver and place those is pretty neat... But you definitely can't do what some are suggesting with placing them on anything but stones. Even a shed that large can be lifted from a single point of contact beneath it and spun around, it's wild. My shed though did have thicker flooring with joists every 1ft so I could park a tractor on it. A stone base that is 1-2ft larger than the shed is enough, that leaves 6-12in around the sides. I don't think you should have any concern with termites getting to the shed in those conditions. I would also consider whatever you choose as border - how it will be to mow around for example. My first shed had a nice border that sometimes stuck up too far (the land was not flat) so I couldn't easily mow around it, I had to weed wack it. My latest shed I only have a border on some of the sides because the backside goes down hill a few inches.

3-4in is enough, the sheds base they deliver will be plenty strong and rigid. If your base isn't perfectly flat they adjust the shed and push stone underneath the runners etc.

I would recommend getting huge pieces of thick barrier beneath the stone, that'll ensure nothing comes up from the bottom.