Yes, this math seems more accurate. And for businesses sending _many_ high-dollar invoices, we have custom pricing. (Get in touch at https://stripe.com/contact/sales or email edwin@stripe.com.)
That's really my question - I think there's room for a $5 or $10 invoicing solution (ie, cap invoicing fee at $5 or so). Maybe somewhat simplified. I'd like custom domain as well of course.