A box is going to have more drag than a rail. This is especially going to be true in warmer weather with wet, slushy corn snow. As people hit the box, it will get a layer of water on the top and the surface tension creates this "sticky" feeling. The only thing I can say here is to try to anticipate the grab in these conditions. A structured base will help but sometimes conditions do make boxes just plaim too much work to ride. I have hit them fast on a warm spring day with a lot of water and it was like stomping velcro, sent me cartwheeling off the end of the thing.
Thats basically what happened to me. It was super sunny out and the top of the box had a thin layer of water. I found going a little quicker and pressing my tail helps slide along it a little better. Thanks for the replies ! ^^