Screen problem - constant 'touch' outside physical screen
 

For a couple of days now my Xperia X has been acting up, it may well have been doing so randomly before but it's now constant. I found the problem by using 'Numptyphysics' which is a game that acts like a paint program - you're supposed to drag lines across the screen but if I tap anywhere it draws a line which appears to originate from about 1cm below the bottom right corner with the phone in portrait mode to the touched point. It messes with scrolling and typing and may even be draining my battery (not sure if this is just post update stuff and will return to normal)

Having tried gentle bending, firm tapping nearby and multiple restarts with no luck I'm left wondering if there is there any way to limit the touchscreen size in software so this 'touch' is ignored?

Any other thoughts would also be appreciated :)