That is what I am currently doing.
I've currently deduced the health and sickness of the rival worst. That was a pretty tricky one to figure.
To note that I may be completely wrong with this and there may be another solution that gets us to a better answer than 8 health and 3 sickness. The formula I used to determine the health and sickness of the city was 100x/(x+n)=72 where 72 has been rounded down, x is the health and n is the sickness. Feel free to try a combination that will get to 72 rounded down!
That comes at 6(+2 for diff) health and 2 (+1 from pop) sickness! Meaning 6-8 floodplains in the BFC.
6 health can be obtained via many ways.
Exp + Fresh Water + 4-5 forests
Exp + 8-9 forests
Fresh Water + 8-9 forests
12-13 forests
So in this case, it is LIKELY that the AI will be EXP. 12-13 forests along with 6-8 flood plains is unlikely bearing in mind that all starts NORMALLY have at least three resources. I think from these options that I listed, the most feasible and likely are Exp with fresh water and 4-5 forests or fresh water with 8-9 forests. With 6-8 floodplains, it is very likely that the AI has river access. Floodplains and forests don't generally go together on maps after all which is why I think Exp is a safe guess.
With the rival best, with 91 expectancy, there are a lot of options as well, for the sake of simplicity, I will be assuming 2 or less floodplains as these combinations become more surreal and difficult to come up with and are very very unlikely
91 expectancy means 9 (+2) health with 1 sickness from pop.
18-19 forests
Fresh water + 14-15 forests
Exp + 14-15 forests
Exp + Fresh Water + 10-11 forests.
With this, it is also likely the AI is expansive. Out of the four options above, 18-19 forests is very unlikely. This leaves us with three (relatively reasonable) options and from them, two include Exp which I think is a reasonable guess.
As for averages, those will take a lot more time than what I've spent on this
Hopefully tomorrow after work because I have Wednesday off
