In reality you don't tune your broadheads. You tune your bow to shoot the arrow with the broadheads on it. The tuning process is the same whether you shoot filed point, mechanicals, or fixed balde heads. The whole idea is to get the arrow flying as true out of the bow and downrange as possible.

Sometimes your bow/arrow combination isn't tuned to the utmost and mechanicals won't show it because there is much less blade surface to make the arrow wind plane. You can install fixedblade heads and the arrows just don't shoot well or plane off course. This is corrected by "broadhead Tuning".

A good source of information for tuning processes is Easton's Tuning Guide, a free download on their website.