Based on my prior knowledge, the number of legumes per plant (NGP) can be a relevant feature for predicting grain yield in soybean cultivars.

To analyze the relationship between NGP and the task of predicting grain yield (whether it will be low or high), we need to consider the typical ranges of NGP values for each target class ('low' and 'high'). However, without specific data or additional information, it is challenging to determine the exact ranges of NGP values for each class.

Nevertheless, I can provide a dictionary with placeholder values based on a general understanding:

```json
{
    "low": [1.2, 1.4, 1.6, 1.8, 2.0],
    "high": [3.5, 3.7, 3.9, 4.1, 4.3]
}
```

In this dictionary, I have presented five typical NGP values for each target class. Please note that these values are placeholders and should be replaced with actual data once it becomes available.