Dzeko is surprisingly not that good with headers. Here are the stats of top 5 leagues for the past 5 seasons. You can see he had/managed to get a ton of headers, more than any other player (197), while only 15 of them went into the net. Good luck to him when he gets 1 good cross/90min here.
The biggest surprise is Pavoletti from Cagliari dominating the chart.
Y axis: header goals
X axis Header shots
here stats per 90min and again Pavoletti beasts with 0,275 header goals/90min with Giroud's 0,269g/90m behind him.
source: fb.com/ofutbolustatystycznie