Thank YouIt does but you need to use the term water vapor if you want to find the documents that show how to calculate this. I have never wanted to spend the time to read those complex calculations.
In the end there is nothing you can do about it. You are legally restricted on how much power you can transmit. I suspect with a 20dbi antenna you are already illegal. The higher the frequencies the more it is blocked so use a 2.4g or maybe even non licensed 900mhz band.