Sorry, was supposed to have a link there: https://www.youtube.com/watch?v=tnX8__trqnQ
Also, sorry for the music. This is from a commercial for the guy in the hakama, not a technique study..but its the best I could find on such short notice.
I see what you mean about the arm/hand slapping the mat! I'll try to work on it a bit more. While I'm thinking about it, would you mind giving me a time for me to look at (in my own video) so I have a sure image in mind for what you're talking about with regard to attacking the mat?