I'm not sure it actually makes any difference which roller moves, it's got to be more to do with the distances between them and their positions, which is altered by where things move or pivot from. You need the rollers to be closer together for a smaller lead in and it shouldn't matter how that's done, but from a practical point of view for building the thing it's probably easier to keep them close by having the middle one on a slider.
I'm intending to build my own when I get chance and looked at everything I could find on here - old threads, youtube videos etc - and have decided to go with the center roller sliding. But your design is easier to build out of basic parts.