Based on prior knowledge, we can analyze the relationship between the feature MHG (Thousand seed weight) and the target variable of grain yield for soybean cultivars. 

Typically, a higher seed weight is associated with a higher grain yield, as heavier seeds generally have a greater potential for producing larger and higher-quality plants. Therefore, it is expected that soybean cultivars with higher MHG values will have a higher grain yield.

To create the dictionary with MHG values for each target class, we need to identify typical values for both low and high grain yield.

Assuming a range of MHG values from 10 grams to 60 grams, we can allocate typical values to each class as follows:

```json
{
	"low": [10.5, 11.2, 12.1, 11.8, 10.9],
	"high": [45.6, 49.3, 47.2, 50.1, 48.9]
}
```

Please note that these values are hypothetical and can vary based on the actual dataset and domain knowledge.