Based on prior knowledge, the NGL feature, which represents the number of grains per plant, is expected to have a positive correlation with the grain yield of the soybean cultivar. Generally, a higher number of grains per plant would result in a higher grain yield.

To create the dictionary with typical NGL values for each target class, I will assume the following ranges:
- Low: NGL values ranging from 0 to 200 (with an average of around 100).
- High: NGL values ranging from 150 to 400 (with an average of around 300).

Using these ranges, I will generate a dictionary with typical NGL values for each target class:

```json
{
	"low": [20.5, 53.2, 85.0, 121.1, 189.3],
	"high": [160.8, 215.2, 270.6, 320.4, 375.9]
}
```

Please note that these values are generated based on assumptions and prior knowledge. The actual relationship between NGL and the grain yield of soybean cultivars may vary depending on various factors, such as environmental conditions and genetic variations. Consider these values as reference points rather than exact predictions.