For me, I use a police machine to polish Rain-X into my wind screen. I do not try to save on Rain-X when I polish my wind screen. I use enough to leave a layer that looks like it has mist on the wind screen. Then I use hand and polish off the rain-x nicely. After that, I never use my wiper at all. Light or heavy rain, the water slips away easily even at speeds of 60kmh (unsure if this is fast for some people).
I ain't sure if y'all notice it or not. I have tried various car wash liquid brands and almost none of them can give the wind screen or glass a really good clean. Especially if you park your car under a tree or plant and it rains, you'll get a thick layer of don't-know-what-it-is thing on your wind screen that even wiper wash liquid can hardly remove it. If you have problem cleaning your wind screen or glass, use detergent powder, those that you use to wash clothes, like serbuk Fab. Use those together with a sponge and give the wind screen or glass a good scrub. The dirt will come out good and clean. I use detergent powder to wash my rims too. The dirt comes out quite easily due to it's strength.
After drying up, then apply rain-x or water repellent with a polish machine. It's been working good for me all this while.