They (should) design the cams for the heads, compression, exhaust, intake, vehicle weight, gears and trans type.
If you contact Clay Smith they will want all of that info to give you the best cam for your set-up.
Generally speaking, upping the lift and/or duration on the exhaust side helps the heads flow better because the exhaust side is generally lacking.
Ideally, as a rule of thumb, you want a intake/exhaust flow ratio of 100/75 on your head flow.
Most heads do not achieve this so they cheat it with the cam profile.
This is where split lift/split duration cams came from.
