Almost always when I have this problem the issue is that I have tightened posts too hard further back on the same Cliffy, which in turn make it raise in the front. In a few cases I haven't been able to fix it though.

I have used double sided clear tape and also used mylar over top.

I have many pins with Cliffy protectors. The only one I have trouble with is LAH left scoop. I put mylar over it.

Cliff is a great guy!

I carefully bend it before installing to make sure the front lip is ever so slightly facing down, helps reduce the gap

I do that as I'm forming them too but sometimes they can still flex up when installed. On nearly all of my semicircle protectors I use 3m adhesive tapes, as you know, but even that can give up its hold. They key to 3M tapes is making sure the surface is absolutely free of wax or silicone polishes and then using the included alcohol swab to wipe where the protector will go. Just as the alcohol flashes off peel the tape backing and press the protector down in place and rub down hard. The acrylic adhesive is alcohol and pressure activated. The white sheet from 3M says to allow a 24 hour cure but not a one of us has patience for that
Some, like the mag rings on metallica or the kickouts on WCS94 are particularly hard on my stainless protectors even though installed on perfectly new and flat playfields. The science is simple. As the ball rolls over the same spot the metal protector gets compressed and eventually the molecules can compress no more and they start pushing outwards. This causes warping and the 3M adhesive can't hold against that pressure. This lead me to search for a better material and carbon fiber is it. Due to ts weave structure it cannot compress and cannot warp. However its not suitable or practical in all applications.

Happy Thanksgiving to all my friends here on Pinside- I'm grateful for the friendships!

And we are grateful for all that you do to help protect our pins. And for your great communication. Happy Thanksgiving to you! Oscar