How does Hidden Potential work?

The Second Wave feature offers the following option:

Hidden Potential

As a soldier is promoted, their stats will increase randomly.

This is fairly straight forward, however I'm looking for detailed specifics on the feature. More specifically:

• Does the range of a possible stat increase depend on the characters class and rank?
• What is the range of possible stat increase at each level?

Solution 1:

Soldiers rank and class do not factor into Hidden Potential. When using Hidden Potential, your soldiers receive random boost in addition to their normal class specific boost. In addition, there is a chance they may get boost to their health even if they would not normally get one.

There is no currently known hard values, but, from personal experience, addition seems to range between 0 to 10 points.