Sounds like you have the right idea. I try to use it when it feels most unexpected. I couldn't tell from your wording if you're hitting it back cross court but I launch it with tons of top spin over the opposing net person. It often draws an error if done right. It's something I only try a couple times a match to keep them honest.The offensive topspin lob .... probably not often enough. But I use it when opponent is handling my deep cross court shots as a change up.