What are the requirements to achieve 2 or more stars on a level in Empire Defense 2? I've been looking but can't find anything. I've tried all sorts of things, but I get nothing more than 1 star as a result.

I tried the following in different combinations

• end with 3000 gold
• using only single unit
• using all available units
• end with general full health
• not using any path moves
• using all path moves
• strategic placement of units and path
• upgraded all units before adding new ones
• bought new units and another spot for them
• end each round with spare time