The ride plate makes the boat think its longer, 22' for a 21' boat, and tries to get more (wetted) hull out of the water. Going with a short ride plate is not giong to have the benefits of a longer one. 1/4" Stainless is overkill, and kinda heavy. The ones I have are- 1/4" X 8"w X 12" long from the transom, aluminum, and the other is 1/8" (reinforced w/ angle alum) X 8"w X 12.5" long, also alum. Both have shoes and loaders. They definitly help with the attitude of the boat(s) being adjustable, but reverse does suffer. 2 positions- forward and not fwd.
Hope this helps
Daniel
Mash on it