Thanks a lot, Nekro.
I checked a bit and found out the ITF methodology of calculation of what they call the Court Pace Rate. I can not be positively be sure that this is the exact same thing as the index shown here, but let´s assume it is. In a nutshell they put ball gun in one side, a sensor on the other, and calculate how much pace you can keep. But there is one piece of information that I could not find, which is how far away from impact location are both the gun and the sensor. If they are close, you need to factor in weather conditions, as you said, if not, the measurement already feels the effects of those conditions. I also assume that they measure it with the same balls that are being played.
I found some more data elsewhere that points to the fact that Miami is faster than IW. (
http://www.tennisabstract.com/blog/2016/11/23/the-speed-of-every-surface-2016-edition/) I am still surprised, but fair enough. We repeat things so much that we start to accept them without further thought (
this time I am only talking about tennis).