in advance: sorry my English is not good ... but I would like to try to help.
I do not know exactly from which components Icing sheets exist. I use sugar paper from "KOPYFORM" in my pictures. Guess it's similar? Moisture and humid climate makes these pictures unattractive. I never had a tear of the pictures. I also do not flood them with RI to fix the picture. I use very sparingly a thick frosting as a substrate so that the pictures stick. Thus, they are dry quickly and have "no time" to blur or tear.
My frosting: powdered sugar and very little water. The mass should be quite thick. I then distribute this very thinly with a knife on the cookies and attach the sugar image. Thus, the cookies are not too sweet!
Maybe this will help you, dear Sabrina?