Based on prior knowledge, the number of grains per plant (NGL) can be a good indicator of grain yield in soybean cultivars. A higher number of grains per plant generally results in a higher grain yield.

To generate the dictionary with specific details, we need to analyze the relationship between NGL and the grain yield. 

Assuming that a high grain yield corresponds to 2000 or more grains per plant and a low grain yield corresponds to less than 1000 grains per plant, we can define the following ranges:

- Low NGL: NGL < 1000 grains per plant
- High NGL: NGL >= 2000 grains per plant

Based on this analysis, here is the dictionary with typical values:

```json
{
	"low": [750.5, 830.25, 925.0, 950.35, 975.15],
	"high": [2050.0, 2225.75, 2367.5, 2410.6, 2550.2]
}
```

These typical values represent NGL values that are likely to be associated with low and high grain yields in the soybean cultivar. Please note that these values are just examples and may vary depending on the specific cultivar and environmental conditions.