```json
{
	"low": [0.0, 4.5, 6.2, 7.8, 9.1],
	"high": [10.0, 11.2, 12.5, 14.0, 15.6]
}
```

Based on prior knowledge, the feature "IFP, plant height" can be used to categorize the grain yield of the soybean cultivar into two classes: low and high. Lower values of IFP may indicate a low grain yield, while higher values may indicate a high grain yield.

In the dictionary, I have provided 5 typical values for each target class. For the "low" class, the possible values of IFP are 0.0, 4.5, 6.2, 7.8, and 9.1 (all in cm). For the "high" class, the possible values of IFP are 10.0, 11.2, 12.5, 14.0, and 15.6 (all in cm).

Please note that these values are just examples and may not represent the actual relationship between IFP and the grain yield accurately. Further analysis and experimentation are required to validate the relationship.