Based on prior knowledge and domain expertise, the number of grains per plant (NGL) can be analyzed to determine its relationship with the soybean cultivar's grain yield. Generally, a higher number of grains per plant would indicate a higher grain yield for the soybean cultivar, whereas a lower number of grains per plant would likely result in a lower grain yield.

To create the dictionary with specific details, including typical NGL values for both the 'low' and 'high' target classes, we can assume the following ranges for the feature NGL:

- Low: NGL values below 50 grains per plant
- High: NGL values above 50 grains per plant

Based on this analysis, the dictionary can be generated as follows:

```json
{
	"low": [10.5, 22.3, 31.7, 40.2, 49.8],
	"high": [51.2, 63.9, 71.4, 82.1, 95.6]
}
```

This dictionary provides 5 typical NGL values for each target class, 'low' and 'high'. Note that the values given are just examples and can vary depending on the actual data and analysis. In practice, it would be important to use actual data to determine the appropriate NGL ranges for each target class.