I was running an email submit for a certain niche, of which COPEAC had 1 offer. I had previously been running an even longer lead gen form, with better results. After some work, COPEAC wasn't able to get another offer in that zip, so I just went on to another site to pull the same offer and test it. My AM said that it wasn't converting nearly as well as other email offers, but I couldn't just switch offers (as there was no other in the niche). I scout out the other networks, find the same offer through another network, and guess what - It converted 5x-8x better depending on what I was targeting! Same exact offer, but I'm guessing the other network had their own pixel on the confirmation page, and not getting batch stats from ValueClick or whoever runs those email submit sites.
I was pretty much just told that "some offers just don't convert well", and it was left at that. To my knowledge, no attempt to figure out why it was tracking lower ever occurred at COPEAC. Pretty much, it was just a "well, try another offer" response.