A puck of smaller diameter may direct the flow to the center of the pellet but it does that by restricting the flow. I am talking about pellets with 5.5 and 6.32 mm., puck orifices are either below 3 mm or full bore 7.3 mm
I am not sure that puck moves towards the plate.It may happen with restricted ones, but not with the full bore one. I understand that pressing the magazine towards the barrel would not help the magazine to rotate.
As Cranky1 says I believe a smooth transition would improve system efficiency, and puck nozzles should concentrate the air from the 7.3 mm of the valve orifice to the corresponding caliber plate orifice (5.75 mm in the specific case of 0.25 caliber)
I will try to get produced some conical pucks and see what happens.