Based on prior knowledge, we can analyze the relationship between the feature "IFP, plant height (cm)" and the task of determining the grain yield of a soybean cultivar as "low" or "high".

Analyzing the relationship:
- Generally, taller plants tend to have a higher grain yield, so we can expect a positive relationship between plant height and grain yield.
- However, there may be an optimal range for plant height that maximizes grain yield, and going beyond or below this range could result in a decrease in yield.

Now, let's create the dictionary with possible values of the feature "IFP" for each target class. We will include 5 typical values for each class.

```json
{
	"low": [15.2, 16.8, 14.5, 16.1, 14.9],
	"high": [20.3, 18.9, 21.2, 19.7, 22.1]
}
```

Please note that these values are just examples and may not represent the actual range of values for the target classes. They are used to demonstrate the format of the dictionary. Actual values should be determined based on specific data analysis.