Analyzing the relationship between the feature 'NGP' (Number of legumes per plant) and the target variable 'grain yield' requires prior knowledge about soybean cultivars and their yield potential. Generally, a higher number of legumes per plant indicates a higher potential for grain yield. Based on this assumption, we can analyze the relationship between NGP and grain yield as follows:

Analysis:
- 'Low' Grain Yield: In this case, we can expect a lower range of NGP values. This can be due to factors such as poor seed quality, nutrient deficiencies, disease or pest infestation, or suboptimal growing conditions. Thus, lower NGP values would be reasonable in this case.
- 'High' Grain Yield: A higher range of NGP values can be expected for soybean cultivars with a potential for high grain yield. This would indicate healthy plants with optimal growing conditions, well-suited genetics, and efficient nutrient uptake.

Based on this analysis, we can create a dictionary with 5 typical NGP values for each target class ('low', 'high'):

```json
{
	"low": [2.0, 3.0, 3.5, 4.0, 4.5],
	"high": [4.0, 4.5, 5.0, 5.5, 6.0]
}
```
Please note that these values are hypothetical and should be adjusted based on actual data and domain-specific knowledge.