Because the equation for cooling capacity is 𝐶𝐶𝑖 = 0.6 ⋅ 𝑠ℎ𝑎𝑑𝑒 + 0.2 ⋅ 𝑎𝑙𝑏𝑒𝑑𝑜 + 0.2 ⋅ 𝐸𝑇𝐼, you’re right that 𝐶𝐶 is dependent only on shade, albedo, and evapotranspiration, and will always be between 0 and 1.
This is only guaranteed if your Kc values are all between 0 and 1. They usually are, but I have seen a couple of sources that give Kc values > 1.
IMO, saying “35% of the heat is being mitigated” is inaccurate because CC does not measure heat. According to Wikipedia, absolute CC is measured in watts. The model uses a relative CC index which is unitless. If you’re interested in the change in heat, the estimated air temperature rasters in the intermediate folder would be a better measure of that.
Even if you do use temperature values, I would avoid talking about a percent change in heat. In a technical sense, 0 degrees does not mean 0 heat, and this is entirely relative to the arbitrary Celsius/Fahrenheit temperature scales that we use. And even if it was possible, a “100% mitigation of heat” is not at all desirable!
For both CC and temperature, I think it would be better to describe them relative to another value. For instance, you could use an average CC value from an undeveloped area outside the city as a reference. If that CC was 0.8 and the CC in an urban area was 0.2, you could say that “The cooling capacity index in the urban area is 25% that of the undeveloped area”.
If a pixel has a CC of 0.35, I think you could also say that “The CC index here is 35% of the maximum”. Again it would probably be more helpful to phrase this relative to a desired CC index. And because the 𝐸𝑇𝐼 is relative to the maximum 𝐸𝑇0 in the area of interest, I would make sure that your area of interest is representative and doesn’t have any strange outliers.