I have the viper with the rail as well. I have found that the rail can be a problem with your knees too. The way that I have solved this problem is:
Adjust the seat straps so that the seat sits as low as possible.
Keep the front part of the seat adjusted a little lower than the back part of the seat as this will allow for your knees to run downhill and under the rail.
Also leave your platform a littl lower and further away so that you are almost in a standing position and you dont have far to go to stand up.
I have been hunting with my summit now for 3 years and it is NOW the most comfortable stand I have ever had and would not trade it for anything.
Hope this helps.

Kill em' Wide and High!!!

Steven J. Collins (Trock63)
Bowdaddy Productions