How to center the changing banner ?

Hello folks,
I am having a hard time trying to center the Inneractive banner on the top of my portrait screen. Here is what I had for my config:

content =
{
width = 480,
height = 800,
scale = “zoomStretch”,
imageSuffix =
{
["@1-5"] = 1.5

}
}

this is rather standard.
Now here is where the problem kicks in, I use:
ads.init( “inneractive”, “this is the app name I registered”, adListener )
ads.show( “banner”, { x=0, y=0, interval=30 } )
The ad banner shows up without any problem, but after a couple of iterations, I found out some ad banners are smaller, for those smaller banners, my right side of the banner display area will have nothing and does not look professional at all. I am not sure how to center these smaller banners without first knowing its size. Any pointer will be appreciated.

btw, I realize Inneractive supports 2 sizes for Android phone (300 x 50 (XL)-- 320 x 53 (XXL)). I was hoping the ad banner will scale to fill to the display boundary on the right side but it doesn’t.

[import]uid: 123046 topic_id: 27931 reply_id: 327931[/import]