I'm pretty sure that Lindbloom (who I also played around with) uses PC levels. Maybe I'm thinking about it wrong, but 100,50,50 is different for PC level 0-255 than video level 16-235.
In other words, when you use Lindbloom's calculator, you are getting an x,y output based on 0-255.
Maybe I'm crazy. At this point I have looked at it too long and need to take a break.
EDIT: Nevermind, just saw you can use it with normalized 0-1. I got the same xy you got with 1, .5, .5...