So if 5 designs only sold 400 because that was the size of the market for 5 designs, then we would've made less for the forum than if 15 designs would sell 600.
Yes there is an overhead of creating the screens per design, but this is why each design that gets produced must be viable by itself. If a design has enough demand to cover the cost of the screens and produce a profit (however small), then it gets made.
Really it's units.
So if 5 designs only sold 400 because that was the size of the market for 5 designs, then we would've made less for the forum than if 15 designs would sell 600.
Yes there is an overhead of creating the screens per design, but this is why each design that gets produced must be viable by itself. If a design has enough demand to cover the cost of the screens and produce a profit (however small), then it gets made.