Based on prior knowledge, the Thousand seed weight (MHG) can be a determining factor for the grain yield of soybean cultivars. Generally, a higher thousand seed weight indicates a higher grain yield potential. In order to determine the appropriate ranges of values for MHG, it would be helpful to have some context or reference range specific to soybean cultivars.

Assuming an approximate range of MHG values for soybean cultivars, we can proceed with the analysis. Here is an example dictionary that includes 5 typical MHG values for each target class:

```json
{
	"low": [21.3, 22.9, 24.1, 25.6, 27.2],
	"high": [32.8, 34.5, 36.1, 37.6, 39.2]
}
```

Please note that the values provided above are hypothetical and might not accurately represent the actual relationship between MHG and grain yield without considering specific context or domain knowledge.