This is a small survey. Regardless of what string you're using. Let us know what tension you're using. Most models are warranty upto 26lbs. I'm sure someone did try 30lbs before..... Let's start ... also do you observed the top frame sink down due to weak design...just survey.
28 x 28 LBS BG66 If your frame sinks in, you can ask for a replacement, it is manufacturing fault. Thanks.