Humm, I tested the seat heaters when I drove the Limited and thought the heat was both back & bottom. Sure hope that's the case cause when I ordered mine I had to pay for leather because I wanted seat heaters. If it's only the bottom .. I'm going to be very disappointed.
Most vehicles with heated seats also heat the lower portion of the backrest as well - makes them great for longer trips when you're getting a little stiff. I'd be surprised if the RAV4 wasn't the same way.
I know for sure because I was in my Rav with the seat heater on 5 minutes ago. They definitely heat both the bottom and the back and it sure feels good. First day of spring today it was still well below freezing this morning.