The problem with using the large plate for 9mm sized cases is that there is more room between the outside circumfrence of the plate and the wall of the casefeeder. Depending on where you have the little clearing block positioned you can have problems. What happens is there is enough room to let another case get down in between the feed plate and the wall. Basically two cases can squeeze into one slot and when they get to the clearing block they can get by and then the feed plate will jam and the motor will be stopped.
I am reminded of this everytime I forget to change the