Based on my prior knowledge, I can analyze the relationship between the feature IFP (plant height) and the target variable of grain yield for this soybean cultivar.

Generally, a higher plant height tends to indicate more vigor and potential for higher grain yield. However, there may also be a limit beyond which taller plants may become less productive due to increased vulnerability to lodging (falling over). Therefore, we can expect to see a positive correlation between plant height and grain yield up to a certain point, beyond which the relationship may become negative.

To create the dictionary with sample IFP values for each target class ('low' and 'high'), I will need to make a few assumptions about the specific values of IFP for each class. These assumptions are based on typical observations and can vary depending on the specific cultivar and environmental conditions. Here is the dictionary:

```json
{
	"low": [10.5, 13.2, 11.8, 12.1, 9.9],
	"high": [19.3, 17.9, 20.2, 18.5, 21.1]
}
```

Please note that these values are for illustrative purposes and may not accurately represent the actual range of IFP values for the 'low' and 'high' yield classes.