php imagick setGravity function doesn't work with compositeImage() function

I'm using php Imagick class for a project

I try to composite an image changing the gravity of the image

What I mean is, I want to composite the target image to middle or to the top center

I use

....
$imageOrg->setGravity(imagick::GRAVITY_CENTER); //I wrote this for an example, position will be set by the visitor
$imageOrg->compositeImage($over, Imagick::COMPOSITE_DEFAULT, 0, 0);
....

But either setGravity() or setImageGravity() functions don't work.

Please help!