Based on prior knowledge, the plant height (IFP) can be an important factor in determining the grain yield of soybean cultivars. Higher plant height could indicate better sunlight exposure and potential for larger yield, while lower plant height could indicate lower vigor and potentially lower yield.

To analyze the relationship between IFP and grain yield, we can look at historical data or perform experiments across different IFP ranges to understand how the target variable (grain yield) is affected.

Based on the given task, we need to determine the appropriate ranges of IFP values for the target classes 'low' and 'high.' Since we don't have specific data or threshold values, let's assume the following ranges based on general knowledge and observations:

- 'low' grain yield: IFP less than or equal to 50 cm
- 'high' grain yield: IFP greater than 50 cm

Using these ranges, we can create a dictionary with the IFP values for each target class:

```json
{
	"low": [45.0, 42.3, 50.0, 49.1, 43.8],
	"high": [65.7, 60.2, 74.5, 67.8, 69.9]
}
```

In this example, we have included 5 typical IFP values for each target class. Please note that these values are arbitrary and would require actual data or analysis to determine the most accurate and representative values for the given task.