I'm not too sure about that mold but I've got the 3.5" version and when mine dent I'm doing one of two things. 1st is I am using too hot of plastic. Second the mold is too hot. Mold being too hot May be fine for some people but I'm very impatient and I demold really fast. I can't explain why those two things cause it to dent but I'm sure someone else can -Jeremiah @bullfroglures