Phaser custom polygon body weirdness

[Secretmapper]

I have a game wide level (800 x 600) which I put at 0, 0. It works as expected, and the level, 'covers the entire screen':

 

 

Now the problem comes when I set the polygon of my level. You will notice that I uncommented line 2 from var level (level.body) and now the level is magically at the center of the screen:

 

Is this expected behaviour or what? Also what is the recommended exporter for Physics Editor?

 

Thanks!