You can definitely use a more aggressive offset than +30, but it really all depends on how simple you want the installation to be. 11" +30 is an absolute guaranteed fit.
As an example, I've installed an 11" +25 wheel with a 305 Michelin PS2 tire on an E92 and had rubbing issues. I've tried the same with Advan Sport tires in a 305 size and also had rubbing issues, so when someone asks me if an 11" +25 wheel with a 305 tire will work 100%, I cannot say yes.
Will it work? Absolutely. Will it work every time, with no adjustment? I can't promise that.
It all comes back to how much you're willing to play with tire brands/sizes/ride height/alignment.