Thanks edhe, I guess I'll have to keep half inching! I've been neglecting it to be honest because it so rarely hits (less than 10% I'd say) and has never got me an rare item. I've found it more fun to pound through battles as fast as possible, picking up dropped items as they appear. The success rate might not be higher than 10% thinking about it, but the gameplay is more rewarding!
What I haven't done yet is let more than one character learn half inch. I'll work on that.