Proposed "more reaslitic" version using same scale:

Desert - Arid - Savannah - Tropical - Oceanic - Continental - Alpine - Tundra - Arctic

(percentages in relation to position on scale)
Desert = 80%:60%:60%:40%:40%:0%:0%:0%:0%
Arid = 60%:80%:60%:40%:40%:0%:0%:0%:0%
Savannah = 40%:60%:80%:60%:40%:0%:0%:0%:0%
Tropical = 0%:40%:60%:80%:60%:40%:0%:0%:0%
Oceanic = 0%:0%:40%:60%:80%:60%:40%0%:0%
Continental = 0%:0%:0%:40%:60%:80%:60%:40%:0%
Alpine = 0%:0%:0%:0%:40%:60%:80%:60%:40%
Tundra = 0%:0%:0%:0%:40%:40%:60%:80%:60%
Arctic = 0%:0%:0%:0%:40%:40%:60%:60%:80%

The problem with this (unlike the original mod) is that it significantly limits those who can inhabit Desert and Arctic climates:

Desert:
80% x1
60% x1
40% x1

Arctic:
80% x1
60% x1
40% x1

Compare this to...
Arid:
80% x1
60% x2
40% x1

or

Tropical:
80% x1
60% x2
40% x2

With the above changes, this means that there would be significantly more competition for species that live in temperate climates than those that live in extreme climates. This might be a desireable effect for some (and arguably more realistic), but it also breaks game balance.

In conclusion, if I do impliment these changes, it would have to be as a seperate mod.

This original mod is fine as is, so a seperate mod would be more ideal