Based on my prior knowledge, the feature "IFP, plant height" can have a relationship with the grain yield of soybean cultivars. Generally, taller plants tend to have higher grain yields due to their ability to capture more sunlight for photosynthesis. However, there might be an optimal range of plant height beyond which further increase in height may lead to decrease in grain yield. Determining the appropriate ranges of values for plant height would require more specific information about the soybean cultivar and the growing conditions.

Here is a dictionary based on the analysis:

```json
{
	"low": [50.0, 52.0, 54.0, 57.0, 59.0],
	"high": [68.0, 72.0, 74.0, 77.0, 80.0]
}
```

Please note that these are just example values and the actual values may vary depending on the specific soybean cultivar and growing conditions.