How can I make my replacement rear wiper clean the whole screen properly?

Having replaced the rear wiper arm and blade with genuine parts on my Vauxhall zafira 1.6 Life 54 plate after the heavy snow snapped the original, the wiper only makes contact with the screen on the first half of its journey and again on its return. I've removed and adjusted it on the spline twice and tried gently bending the plastic arm using hot water but to no avail.
Can anyone help?