Hello... I am considering turning on placement targeting for some websites. A lot of these sites have mutiple ad units - all on the same channel. So, site1.com - may have one channel, labeled site1; which has a variety of different adsense unit sizes on different pages. Some pages have one sized ad units whereas other pages have different sized ad units... So, is it wise to turn on placement targeting for the entire channel? Or will advertisers be confused because of all of the different ad sizes, pages, and positioning of the ad units on the channel... so, my question is - if I am not able to have a channel have only one ad unit in a fized position on a site - is it still wise to have placement targeting? or, shoudl I only do it for specific ad units that are already defined