I have checked with BAL (Supercover) and they confirmed that when mixed the volumes on Supercover and a 'standard' 20Kg bag are the same. I also rang Tilemaster and their explanation was very strange. They said the mixed volume of Magix is similar, but slightly less than a 20Kg 'standard' bag, but it goes the same because of the glass beads. I struggle to see how this works. If the mixed volume is less and your trowel is the same then you will spread the same volume per m2, so it should not spread as far. OK, if the adhesive is super smooth you will perhaps waste less, but surely not by a significant amount. Perhaps that is why they call it Magic.