We don't know if the ND picture was normal - until we know the tilt setting on the WXR it's difficult to conclude anything, but, I think At the time the FCTM/FCOM says something like" CRZ ALT - set tilt "slightly" negatively down," if that's what actually was set they may have been over scanning and had a false picture. Over water ITCZ type flying needs aggressive down tilts and short ranges(80nm and 3.5 ish down tilt etc)