General: DiscZone center point doing chaos (2D)

This is the code, the DiscZone is instanciated at the 5th line.
This FX is designed to follow a DisplayObject, so the code ends with an addActivity(FollowDisplayObject).
All I want is to have a distance of 50 vertically between this emitter and the object followed.
That's why the Point given to the DiscZone is set to (0,50).
But the result isn't an y offset, the result is the DiscZone having a radius of 50! :(
That sucks badly. Note that I also use an offset for the GravityWell and that one seems to work.
I use this engine for the game Faeria (www.faeria.net), I truly don't regret that I chose Flint as the particle engine, I want to make it shine.
Support highliy appreciated, thanks.

var locRockEmitter:Emitter2D = new Emitter2D();
locRockEmitter.counter = new Steady(20);
display_object_emitters.push(locRockEmitter);

locRockEmitter.addInitializer( new Position( new DiscZone( new Point( 0, 50 ), 20)));
locRockEmitter.addInitializer( new ImageClass( Particle, [Assets.ROCK] ));
locRockEmitter.addInitializer( new Rotation(-Math.PI,Math.PI));
locRockEmitter.addInitializer( new Lifetime(.5) );
locRockEmitter.addInitializer( new ScaleImageInit(.05 , .15) );

locRockEmitter.addAction( new Move() );
locRockEmitter.addAction( new Fade(1,0) );
locRockEmitter.addAction( new GravityWell(300, parCarrier.x, parCarrier.y+100) );
locRockEmitter.addAction( new Age() );

locRockEmitter.addActivity( new FollowDisplayObject(parCarrier, parRenderer) );