Ridgway?

I own the attached plate. Stylistically, it looks like c.1830-5 Ridgway, and the pattern number on the reverse would tally, in that the 6648 pattern number stacks with the Ridgway pattern numbers, but the "4" above the 6648 seems like part of a fractional pattern number-and Ridgway didn't use them. It can't be Spode, Minton, Masons, Coalport, Davenport, Grainger or Flight. Can anyone help?

 

Rockingham?

 

I think Alcock used these fractional pattern numbers and it looks like Alcock style wares.