Based on the given feature description and task, we want to determine how the thousand seed weight (MHG) of a soybean cultivar relates to the grain yield. To analyze this relationship, we can use our prior knowledge to determine the appropriate ranges of values for MHG for low and high grain yield.

Let's assume that in general, a higher seed weight (MHG) would result in a higher grain yield. Based on this assumption, we can infer that for the "high" grain yield class, the MHG values would be higher than for the "low" grain yield class. 

To create the dictionary, we need to include 5 typical MHG values for each target class. Let's assume the following values:

For the "low" grain yield class:
- [30.2, 32.1, 33.8, 29.5, 31.7]

For the "high" grain yield class:
- [36.9, 38.4, 37.2, 39.1, 37.8]

Now, let's format the dictionary in the required schema:

```json
{
	"low": [30.2, 32.1, 33.8, 29.5, 31.7],
	"high": [36.9, 38.4, 37.2, 39.1, 37.8]
}
```