You'll get better FM reception if you place your antenna in the attic, not the wall. You would get even better reception if that antenna were placed on your roof but, understandably, many people don't want to do that,

Wire your antenna with RG6 coaxial cable.

Look up your FMFool.com report from the link and post it here: that will give us a much better idea of what kind of antenna you'll need to use for best results.

Here is a link that might be useful: Link to FMFool.com