Rear defroster

I had the back window replaced in my 2000 z24 due to a tree branch last winter and thought it would have solved what i thought was a problem. the rear defrosters really suck. they never really work the way they should have. I had a 93 and 94 plymouth sundance and they worked great, i got this car and was very disappointed in the performance. Am I the only one that has this problem or is it a bad design by GM???