I had the same question. I changed the jig head and placed a treble stinger over the eyelet of the jig head and then placed the whole thing inside the tube jig- so the stinger was in the skirt of the jig. After that, perhaps it was coincidence, they didn't hit the jig. My suspicion is that the stinger changed the action enough to make them cautious. I removed the stinger and they started biting it again.
My main idea, after all of this testing, is that a tube jig head with hooks on both front and back might be great - similar to a jigging Rapala with hooks on each end. If the bite is slow, I see MANY times that the fish bite on the tube jig head first and then spit it out before they reach the hook. A double hooked jig might catch some of them.