Scaled it up a bit (to 130%) and it came out quite nice, but it's a really, really tight fit.
Spend some time sanding the inside of the sleeve, and the surface of the maze, and now it works very well.
I'm giving this one to my brother... I'll report the time he'll take to unlock his present :-)
I'll try and scale the inner and outer parts 1% off next time though, to save me from sanding.