Generally the ‘E’ and ‘I’ laminations are extremely efficient in material usage, as the stamping overlap so there is no wastage of materials… If they are wasting material then why not use a ‘C’ core where the lamination is a continuous strip so no wastage again? Or better still a toroidal core using a strip of material as the lamination – the winding maybe slightly more expensive but the core is much easier to make and more efficient. Your question at the end about how core shape influences short circuit current isn’t really related to your body text… Please explain what it is you are asking… John