See that thing? Yeah, that. Whatever that is. Right-click it. Anything happen? No? Try that other thing.
You know the itty-bitty little drag handles that are the correct way of doing audio crossfades (rather than the hair-brained bastard transition nonsense Dza favours)? Right-click that.
Win. And yes, the constant-power +3dB fade is default, as is right and proper, but there are times when a long tail -3dB is called for.
I've never used a linear fade.