From my side, it started making more sense after messing up a couple of panels during grad school. IgM just behaves differently because of its size and shape, and secondaries don’t always “see” it the way we expect. I stumbled across an explanation while double-checking the lgm full form and it lined up with what I’d seen at the bench. Big molecules look impressive on paper, but in real assays they can block access or bend in awkward ways. Honestly, once I stopped treating IgM like IgG’s cousin and more like its own beast, my results felt less random.