Ice can only "block you later".
As for blocking Masters, your best bet is to not pay much attention to what they are doing. If they have tells, they know it and will use it against you. Focus on what you are doing and run your "D". Knowing what hole they are most comfortable shooting helps. For instance, a pull shooter that has a great long like Tracy McMillin. Most of the time his focus is reading when the long will be open. Because I know this, I will shuffle around in the straight and middle, then dart out to the long. If he starts reading me comming out of the long, dart to the long and wiggle, but don't move out of it. This will usually get a few blocks until he adjusts. Then I change to something that "looks the same" but do something different. If he starts reading me when I dart to the long and shoots middle, then I fake moving to the long and stay middle. Like you said, it's a percentage thing. If they are really messing with me, I'll start making myself do the oposite of what I "want to do". Block like a beginner for a few posessions. Then start a different progression of defence. If you are playing a master at a draw or in the losers bracket and it's 2 out of 3, there probably isn't time to try random stuff for very long or the mach will be over before you find out what works. Tracy has given me a few tid bits that have helped tremendously. I think the best thing I would say is to "shorten the hole". What I mean is to learn to stop your 3 man goalie a little less than 1/2 a ball legnth from the edge of the goal. That way you have kept more of the goal area with a man in it. If you go all the way to the wall, you have left a much bigger split. This is kind of hard to explain without showing you on a table, but I think you can figure it out. You are also right about being fluid in your movements and not being tight.
Hope this helps!
And I'm sure Ice will chime in with something good!