Screen touch doesn't feel right - everything looks fine.

Recently I have stumbled across an iPhone 5s which I cannot seem to fix. When I fit a new screen the touches don't feel right. The screen displays fine and the touch works everywhere, however you need to swipe with a big surface area, such as your thumb. If I use my index finger the screen won't respond, when I tap an icon it works, if I try to swipe around the settings/springboard it doesn't. If I keep my index finger on the screen for a while then swipe it works fine.

I tried 2 new screens, and 2 broken LCDs. Both of the broken ones where fine.

I'm guessing the 2 new screens come from the same batch and are both faulty?

The problem just seems so odd.