Filter of Ecostyle 61 casts shadow on back

[Soulsarfar]

Can someone please advise? I've had my tank for a while and have only just got a background for it. Now I've noticed that the top third of the background has a horizontal shadow caused by the filter going right across the back. Is there something I have set up wrong or is this just purely bad designing on their behalf?
Thanking you in advance.