Ryokan room paying customs

I dont want to slip on this, since ryokans can be veery expensive and one thing looks strange to me. For instance here:
http://www.aura-tachibana.com/english/room/index.html

For a room (of max capacity of 6ppl, japanese style room) prices (''Rates from 15900 Yen per peson / a night'') are given.

Now that is very fishy, because (imo) it suggest, that I with a friend (2ppl) can rent a whole 49m2 room and have it exclusively for us, by paying only for 2 ppl? I really dont want to end up being asked to pay for 6 peoplel just be cause we (2 people) reserved a room.
So question is: is it normal for ryokan room reservations to get a whole room regardless of the number of guests? And is it normal to pay only per physical, real (xD) person per night or can I expect a bill for all (also unused) slots in a room?
Thanks in advance.

is it normal for ryokan room reservations to get a whole room regardless of the number of guests?

Yes, but the cost per person increases. That is where the "from" comes into play.

But don't worry, the cost will not be three times higher in case of double occupancy . It might be 20% higher or something like that. If you follow the "Reservation" link, you will find actual prices, including some discounted plans.

And is it normal to pay only per physical, real (xD) person per night or can I expect a bill for all (also unused) slots in a room?

The cost given when you book on the website.

Go to 'the reservation' on the Tachibana website where you see the various plans for two persons for your choice of room type.

I see three or four different type of plans. The lowest is 10,000 per person without dinner or 13.900 with dinner. Dinner at ryokan is another venture for you. I would take 13,900 yen plan. Otherwise, if you two are on honeymoon, take the couple plan regardless how much it is.

The rate is usually shown per person. You do not have to pay for three or more. Upon the reservation, the price you will pay is fixed. No additional charge for the room.