Attic installations are always dicey.
My advice would be - if you aren't happy with performance - move the antenna to the roof. At attic height, you might be aiming through trees, and multipath through the trees will get worse if it's wet or windy. You have lots of signal to work with, and all the stations of interest are closely grouped. The C4 is a fine antenna, and you could add the dipole kit to get WHAS... but you might not need it in free air.
You could try moving the antenna around in the attic. But that's just looking for a chance improvement - no guarantee anything will change.
Sounds like your problem is signal quality at that location, not signal strength. Take a look at this link
http://www.hdtvprimer.com/antennas/siting.html to get an idea of what's going on with diffraction, ground reflection and trees.