I received an email from Carolyne in Canada, but was unable to email a response back. So I figured I'd answer her question on my blog since others probably had the same question anyway.
1. If you like your injera to be more sour, you can use a self-rising flour starter instead of adding it fresh on the day you cook it. This will add sourness. Also, allowing more time between feedings of a starter adds sourness. But you have to be careful because if you allow it to sit for too long without feeding it, some of the yeast begins to die and you won't have as much ain.
2. If you are only able to get good ain on some parts of the injera, it could be due to your heat. Injera depends on high, fast heat to force the CO2 that is released by the yeast "eating" the flour to come to the surface, thereby creating ain. Also, it could be an issue of not having enough active yeast to begin with.
3. When you cook your injera, if it gets slightly crispy on the bottom, it should soften after it cools.