Hi,
my L1520 was falling flat on the ground (real tiles) twice. It is still not damaged. I have a nilkin tempered glass screen protector and maybee some luck.
If a case adds torsional rigidity it would help, IMHO, as the issue has pretty well been identified as flex related. Although there are some who swear it is software.
I had some phantom scroll and tap. Sure enough my phone was out of true and the TPU case I had did nothing to prevent that. After carefully straightening the phone my phantom scroll tap went away. YMMV
http://forums.windowscentral.com/nokia-lumia-1520/297759-6.htm
How did you straighten it?