Ok, I've checked my board game rules (1989) they don't say that your move must end off board to be off board.
They says that if you fly off board you have escaped (only if you fly off board along your board side obiouvsly).
So for me it's a matter of how do you intend the term "flying off board".
I suggest that the moves that partially goes off board should be prohibited. The board's edge are part of the game, you have to consider them and plan your move in order to stay into the board or take into account flying off board.
Maybe we can start a poll about this in order to know what the other users thinks.
All trademarks or tradenames used in this Web site are the property of their respective owners. Material may not be republished, nor may content or images be mirrored on another server without written permission.