This does not calculate properly and i wonder why?
It doesn't possibly because Stardock uses a billing company which probably has different rates for different volumes of business and Stardock probably averages the costs, discounts, etc. so as to not pay more per transaction while still encouraging folks to buy its product. That's just a guess, though. I don't know that's how a price is arrived at. I would assume though, it isn't a random number.
It's logical when you see that one single transaction will cost Stardock less in billing fees than more than one transaction to do the same thing, but again, that's just conjecture.
I'm not speaking for Stardock, but rather as someone who used a billing service in the past. Stardock's situation might well be different than mine was, especially when considering the volumes of business, respectively.
I can tell you as someone who's been here 20+ years, that Stardock gives good, and fair deals and cares about and for it's customers.