8x10 sheets are about 20x25 cm, so not much bigger than 18x24.
If you are working with 8x10, that 450 figure will be reduced to about 390 - not 2430.
Film has a lot more silver in it than paper does, so it wouldn't surprise me that the area of paper that can be fixed is four times the area of film that can be fixed.
Note especially the discussion about different capacities for "general purpose" and "optimum permanence" as well as the shelf lives for various dilutions and amounts and the discussion of two-bath fixation.