Pay closer attention to how the screws interact, they are not the same device. The force vectors are applied in different directions depending on the order in which the screws are turned.
And it depends on the palate. Some may need even expansion across the whole palate, while others may only require force at the front or back of the palate.
So, for example, if the front of the palate/teeth are properly round and the palate caves inwards towards the rear teeth, then the modified expansion device would be unsuitable: It can not be used to expand at the rear without also expanding the front. The acrylic behind the canine teeth moves out just as far as the acrylic behind the molars.
Where as with, say, the Y plate one can expand the rear without moving the front, or also expand anterior forward while leaving the posterior as it is.
Use your tongue and how it fits in your mouth to see exactly where you need to put force.