Based on my prior knowledge and analysis, the feature "IFP, plant height" (cm) could have a significant relationship with the grain yield of the soybean cultivar. Generally, taller plants tend to produce higher grain yields. However, there might be an optimal height range beyond which further increases in height may not necessarily result in higher grain yields.

To create the dictionary with the requested format, I will include 5 typical IFP values for each target class, "low" and "high". Please note that the specific values will depend on the dataset and any available information.

```json
{
	"low": [25.5, 26.2, 24.8, 23.9, 26.7],
	"high": [39.8, 40.5, 38.9, 41.2, 39.1]
}
```

These values are just examples and should be replaced with actual values derived from the analysis of the dataset.