I normally don't have trouble with craters with the icing recipe I use. However, a few weeks ago I was working on some cookies and was filling in the lettering on the logo. I was flooding very small sections, just as you described. I experienced the worst cratering EVER.... in all 12 of the cookies I made. I scraped out the flooded areas (as they hadn't fully dried), and re-flooded, being sure to flood them extra full and run a toothpick through the icing this time, but I STILL had cratering problems. I actually had to go back later with icing on a toothpick and carefully try to fill in the craters - it was a nightmare! Out of curiosity, I took the same icing and flooded several 3" circle cookies to see what would happen. Those cookies had NO cratering problems whatsoever. So, the only thing I figured out was that the icing was fine, but something about flooding in those small areas was causing the cratering issue. Next time I will have to try the dehumidifier idea that some of you mentioned above..... maybe that's the secret! Thanks for the idea!