The flipper needs to be above the horizontal by at least 30 degrees and unpowered when the ball makes contact with it. How do you get an unpowered flipper to 30+ degrees (this can vary slightly depending on the rake of the machine) ? Simple; you have to press the flipper button as the ball is approaching the flipper and then release it just before the ball gets to it (and then obviously reinstate the power after the ball is caught on the flipper for a shot or cradle).

As opposed to a live catch where the power is never released.

When a flipper button is pressed and held, the flipper will reach its maximum position at a particular moment in time. If the ball makes its initial contact with a point along the flipper at that same moment in time a live catch will occur.

The more inward the contact point, the more precise the timing must be for a live catch. But why make things hard on yourself ? Drop catches are much easier and can be cradled if the ball is traveling towards the inside of the flipper.

It's a "just-in-timer" (critical for red/yellow-flipper rubber games)