This is the system of levels I have used in my fiction. It is based on the idea that the feelings associated with compatibility are like the human senses — they show a logarithmic response. Two sound twice as loud, the actually sound energy must be much greater. To make this easier for the reader I have used base 10 logarithms, but I don’t know how realistic that is. The image below summarizes my notion that compatibility is related to pool size: the large the pool of candidates to choose from, the more compatible the best will be. Red arrows represent incompatibility, perhaps even hostility.