Based on my prior knowledge, the thousand seed weight (MHG) is likely to have a positive relationship with the grain yield of soybean cultivars. Higher MHG values generally indicate larger seeds, which can lead to higher yield.

To create the dictionary, we need to analyze the relationship between the MHG feature and the target variable (grain yield) for both the "low" and "high" classes.

```json
{
	"low": [150.0, 180.0, 160.0, 140.0, 170.0],
	"high": [200.0, 220.0, 240.0, 210.0, 230.0]
}
```

For the "low" class, these are 5 typical MHG values: 150.0, 180.0, 160.0, 140.0, and 170.0.
For the "high" class, these are 5 typical MHG values: 200.0, 220.0, 240.0, 210.0, and 230.0.