I’m guessing that saying “tight corners” makes someone pull back rather than pushing forward. I also tell students that they want to think of a “ewwww” sound, or an ü or something of that sort. But it does take time for some students to really get it. I can’t tell you how many times I have to say “corners forward” when I teach!
I also show them the picture in the book by Jay Light, that shows an anteater (correct) vs a cabbage patch doll (incorrect). I tell them that while it looks like we are pulling back sometimes, it never feels that way.
Sometimes, with my little ones, I suggest that they “kiss the reed”. That helps them understand we don’t bite. Sometimes.
I’m sure others will have better solutions, but there are just a few things I talk about.