Better way to make Iced Tea
The advice I have heard is for stronger tea use more tea.  Do not steep longer as it can get bitter.  

If you are in a hurry a stronger tea with ice could work but if you want to come from brew temperature to ice temperature it would need to start very strong.  

Maybe experiment with double strength and let it cool to like 100 F. You would add as much ice as tea. If all the ice melts then you need to let is cool more next time. If almost none of the ice melts then you need to let is cool less next time.