Try taping a "ruler" style piece of paper to the top of your flippers.
And then figure out the right location of the ball on the flipper to get your timing down.
You will see that the location differs based on the speed of the ball.

I've done similar without hitting the ramps much at all. Currently have GC on our local one, and I can't hit the right ramp to save my life. There's a lot of ways to score without them, but as far as hitting them goes, you have two separate cases here:
1. Hitting them from a trap
2. Hitting them as the ball comes down the inlane from the other ramp

You can technically make due with just #1, but you're going to spend a lot of time trying to get a trap before shooting the ramp again.

At the same time, you don't need to shoot both ramps! Watch the NYC Finals on youtube. Bowen Kerins didn't like shooting the right ramp, but figured out the timing on the left, so he'd just shoot the left, hold up the left flipper, bump the ball over to the right, and shoot it again. I haven't tried that technique but I also find the left ramp easier to hit than the left (and the designer, Elwin, agrees too)

As far as the actual aiming goes, are you doing something like described here?

It's the only tutorial I've ever come across on aiming, and it's from Tim himself!

In the end though, lots of people make shots in their own ways. It's much harder to teach than other skills (besides nudging maybe), and I feel your pain as accuracy is my weakness too

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