Tilt the gun, if we call the bottom of your pattern the "heel" and the top of the pattern is the "toe", just lean back on the heal and rake the toe up. The toe of the fan pattern is your fade.
If your overlay color doesn't hide well, it will be tough to get a nice fade transition, it can get mottled on you.
Honestly I had better luck fading 2k single stage rather than base coats. I had my best luck wet on wet, 2k single stage metallics.
Get the underlying color on, full coverage. Then hook up to the overlay product, lean back on the heal of the pattern at your part or panels edge and try to get it done with 2 passes over and back 100% overlapping your first pass at the fade transition.
You will probably just have to practice it on some empty paint cans, a fender, an old car hood or what ever you have laying around.
But I had good luck wet on wet 2k single stage because it flowed into itself at the transition which I feel really helped the uniformity of the fade.
How ever you get it done, good luck, post pics.