While you may find a general pattern between area and heat, there definitely isn't a relationship.
Its like saying saying the size of an engine is related to its power output. There are many additional factors that affect an engines power than simply its displacement.
There is a lot more that effects a processors power ouput that its area.
If we knew the die size of the G92b, we could approximate the number of transistors and find out how much heat it would output compared to the G92. From that you'd get a very rough estimate of how hot the 9800GTX+ would be.