Not sure about the two plates. I have only seen the larger plate with 6 (maybe 8)or so holes in it. If you have a choice, I would use the larger plate.
There is a terrific amount of force on that small ball when the trailer tries to turn or sway and the possible slight movement may be too much for the thin steel of the trailer A frame. The "tin canning" of the metal could cause it to fail. The larger surface of the big plate will tend to counteract that.
Barney
Edit: Watch
this video. It explains what the larger plate with 8 holes is for. After watching it, I still maintain it would be best to use it for the reason I mentioned.
2004 Sunnybrook Titan 30FKS TT
Hensley "Arrow" 1400# hitch (Sold)
Not towing now.
Former tow vehicles were 2016 Ram 2500 CTD, 2002 Ford F250, 7.3 PSD, 1997 Ram 2500 5.9 gas engine