How to slide a window for 90% to right without to see it compressed

Question

I ve tried this piece of code to make a slide-to-right animation on a window (it's is a common way.. but usually the slide is made for 100% to left/right which makes the window to disappear completely from the screen ) but what i need is just to slide for 90% to the right :

    var slide_it_left = Titanium.UI.createAnimation();
    slide_it_left.left = 0; // to put it back to the left side of the window
    slide_it_left.curve = Titanium.UI.ANIMATION_CURVE_EASE_OUT;
    slide_it_left.duration = 500;

    var slide_it_right = Titanium.UI.createAnimation();
    slide_it_right.left = "+90%";
    slide_it_right.curve = Titanium.UI.ANIMATION_CURVE_EASE_OUT;
    slide_it_right.duration = 500;    


$.menubtn.addEventListener("click", function(e){

 $.index.animate(slide_it_right);
    // newWindow.open(slide_it_left);

});

the problem is that the animation just makes the left edge of the window sliding to the right and maintain the right edge fixed which results on compressing the window on the left(remaining) 10% of the screen Is there a solution to slide the whole window instead of just its left edge and get rid of the compression effect ? thanks for your help.