Dear Dearest of Dears with Beers,
Please increase the energy cap to 20, and then double the income rates and unit costs to compensate.
This will give you much more control over balance, especially with low-cost cards. In essence, this would allow you to make units costs increase in intervals of .5 energy, which in some cases is essential to achieve proper balance.
~ Quack-a-doodle-doo ~