The Sensation has one of the new qHD screens at 540x960 rather than the older 480x800. This is likely why you're not seeing the app scale to full screen. You can try using the Spare Parts Compatibility Mode setting like tablet users to force older apps into full screen (see
here), but that might have other consequences. It can't hurt to try, though. Worst case, it force closes and you have to go back to running it not-quite-fullscreen.