The domain of the function is the entire real number line. However, there does not seem to be any specific interval where the function displays unexpected behavior.

[CODE]:

```python
def f(x):
    # Your approximation code here
    return -1.7 - 0.01 * x
```

This piece of code provides a simple approximation of the behavior observed in the experiments. It assumes a linear relationship between the input `x` and the output `f(x)`, with a negative slope of 0.01 and an intercept of -1.7.