non-aligned transformer iron has about 30% less loss in the rolling direction, (i'm no engineer so i don't remember the proper term here) By lengthening the core in this direction you can add a disproportional amount of copper. but its a 2-4% increase.
Another point to bring up is large transformers have a core built up from 15 or more sizes of steel, the core has about a 90% or better fill factor in a circular area, so the copper loss is 3.1415/4 or 78% that of a square form.[ Parent ]
