Can't find this documented so I don't know if it's normal behaviour.  On my computer the micro-break reminder appears in the middle of both screens, but 5 seconds later jumps to the top of the screen.

I would much rather have it stay in one place, either always appearing at the top of the screen, or always in the middle.  Is there any way to configure this?

This is normal behavior. The idea is that it should be possible to ignore the reminder by just continuing to work. Therefore, after being placed in the middle of the screen to attract attention, it jumps to the top to move "out of the way" to allow you to quickly finish up, or continue working, whichever you choose.

You'll find that if you move the mouse to the reminder window, it will jump out of the way again (this time to the bottom of the screen) to allow you to click any button that might be below the reminder button.

There currently is no way to configure this behavior.

thanks for the quick respose guys, just looked a bit odd :)