Thanks to everyone who responded. I finally chose to use two 6 inch strips of 400 on each side of the plate, one at the front and one at the back. The rest of the plate and ski are covered with clear 250. I have not prereleased since, and I appropriately released once. This seems to work well for me. I really like the feel of the Powershells and am glad it is working for me now.
I would reiterate Klindy's comment to remove the dual lock under the nuts. Also, I have found that a wooden dowel and rubber mallet are useful to fully engage the 250 and 400.
In response to clemsondave, the prerelease issues happened at varied times. Once I was too far on the tail, but the other times I felt like I was in a good position.