Positioning empty movie clip external image loader

Hello (again),

I am building a gallery for a photographer.

The setup: one large mc loader on mainstage (myLoader_mc). Several movie clip thumbnails contained in one large movie clip. You click on the thumbnail, large image loads into myLoader_mc. I am using a purchased component from extend studios for my transitions.

The problem: my jpgs are of different height and width. I want to keep using the same movie clip to load the images (myLoader_mc) but position the loader with different x and y coordinates for each loaded image so that it is centered on the stage. I am using the following script but the loader clip is stuck in the position defined by the first thumbnail. the script is in layer 1, frame 1 of the movie clip containing all of the thumbnail movie clips.

th1_mc.onRelease = function(){
_parent.myLoader_mc.loadMovie("/assets/family/1b.jpg");
myLoader_mc._x = 162;
myLoader_mc._y = 5;
}
th2_mc.onRelease = function(){
_parent.myLoader_mc.loadMovie("/assets/family/2b.jpg");
myLoader_mc._x = 282;
myLoader_mc._y = 5;
}

The image loaded by thumbnail 2 is stuck in position on thumbnail 1. Need to change this dynamically no matter which thumb is clicked.

Any help is appreciated and I hope I have explained this clearly enough. If you help me solve this, i will toast my next drink to you.