To analyze the relationship between the feature MHG (Thousand seed weight) and the target variable (grain yield), we need to consider prior knowledge about soybean cultivars.

In general, a higher thousand seed weight (MHG) is associated with a higher grain yield in soybean cultivars. The heavier the seeds, the higher the yield potential. However, it is important to note that there can be other factors influencing the final grain yield, such as planting density, climate conditions, and disease resistance.

Based on this analysis, we can create a dictionary with typical values of MHG for each target class:

```json
{
  "low": [30.5, 32.1, 29.8, 31.2, 28.7],
  "high": [37.9, 36.4, 38.6, 39.2, 35.8]
}
```
These values are just examples and can vary depending on specific cultivars and environmental conditions.