[Saulot]

Figuring out the probability of there being a lvl 2,3,or 4 site in one specific path when all you've searched is lvl 1 in one specific path is probably impossible. Magic sites are restricted to certain terrains, and unique ones which occur earlier in the map creation restrict future ones from appearing again. Terrain also affects the overall chance of magic sites in a particular location. Without knowing what other sites are in that location, what sites are elsewhere on the map, or considering the terrains on the rest of the map, and the exact method of magic site creation, presents the difficulties.

However, I've done the math before based on likely numbers of sites in a province (bernoulli trials). The chances are of course affected by the default magic-site chance. They are also affected by terrain.

From memory, I believe wastes give 20% higher magic site chance. Forests give 10%. Mountains 15%. Farms -10%. This should confirmed.

(Trivia that everyone should know, lvl 4 is the highest site number, so using someone with more than 4 in a path searching is unnecessary, and 4 is the maximum number of sites in a province.)

Odds of X magic site in a default terrain with 60% chance magic sites

1 = 97.4%
2 = 64.4%
3 = 30.0%
4 = 11.6%

Odds of X magic site in a default terrain with 50% chance magic sites

1 = 96.8%
2 = 49.8%
3 = 18.6%
4 = 5.81%

Odds of X magic site in a default terrain with 40% chance magic sites (default medium era)

1 = 87.0%
2 = 35.1%
3 = 10.1%
4 = 2.45%

Odds of X magic site in a default terrain with 30% chance magic sites

1 = 75.9%
2 = 21.5%
3 = 4.57%
4 = 0.79%

I hope this covers the topic thoroughly.