Adjust football snap size dynamically

Football snaps on fronts to occupy all available height when placed in a "big" container slice.
#### before
![screen shot 2014-08-07 at 15 44 59](https://cloud.githubusercontent.com/assets/1492162/3843575/8c6da232-1e41-11e4-96ec-066a958a8f5b.png)
#### after
![screen shot 2014-08-07 at 15 45 12](https://cloud.githubusercontent.com/assets/1492162/3843581/9267cc76-1e41-11e4-930d-bf79f34e7e6e.png)
![](http://media.giphy.com/media/fEJIHsmeDJZu/giphy.gif)
why not just return immediately if `el` is false, save testing it twice