I can't work out why, but last time I tried with my max authorised size case, I simply could not get it in try as I might (I tried both overwing where I was sitting and near the front, where I was told on another thread the bins were marginally bigger). I don't know what the problem was, but with an impatient crowd (despite being first on the plane) surrounding me, I surrendered and gave it up to be loaded in the hold.