How do tier costs work for more than one full region?

I've been looking a bit closer at tier costs lately and I'm a bit confused about what happens when you get more than an entire region. The Land Pricing pages don't seem to have any info about what happens when you get to that level.

So if I had one full region I'd be paying $195 in tier costs per month. If I then purchased another 1/128 region, would I pay an additional $5 for a total of $200? Or would the tier jump to 2 full sims so I'd end up paying a total of $390? Or something else I haven't thought of?

This would be something I need you to direct to [email]support@secondlife.com[/email] - Thanks!