I read you loud and clear on wanting to master your device's functionality and not worry too much about where you're touching down at the same time. So, let's work on this together.
To be completely honest, there is no setting on your 8X where you can alter the sensitivity of the touch screen. There's no doubt that that we all have to be a little careful at times where we're pressing down or we may not get the desired outcome so I do apologize if this is an inconvenience. But, thank you for the feedback.
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The Verizon rep is correct of course, but I'd like to offer a possible solution; at least one that worked for me.
I have on my htc an "otterbox" defender, which has, of course, a screen protector, then I put another screen protector on the screen of the phone itself, under the otterbox screen protector. This rendered the screen touch input a little less sensitive.
Also since you are in your trial period still...the Lumia 928 has the ability to adjust the sensitivity...granted it would be a completely different phone but if that is another option you want to try.