So I set up several campaigns on Exoclick, each for testing a separate placement type - let's say they were NTV-A, In-Vid, and Homepage Cube. Same bid, targetting same sites and country. When I found that NTV-A was converting the best, I switched the other 2 campaigns to target NTV-A also.
After I did that, however, I noticed a decrease in traffic - it almost looked like the amount of traffic I was getting for the original NTV-A campaign, got spread out across the 3 campaigns after they were all set to target NTV-A.
My questions to the vets:
1)Should I not have set more than 1 campaign to target the same country, bid and placement?
2)Could I have circumvented the problem by staggering my bids for the 3 campaigns? If so, how much should the bids differ by? 1 cent? 10 cents? Or more?
Thanks in advance for helping a newbie out!
Amy
1) This depends on how the traffic source works. If budgets are set at the campaign level, it might be better to split creatives into separate campaigns, particularly if ad performance influences impression serving or you are using a low budget, CPC bidding, etc. Some traffic sources are good at giving very even impression serving to all ads in a campaign.
If you want to send a large $ to a specific ad it is better to have it in it's own campaign.
As for bidding against yourself, if you are top bidder then presumably making multiple campaigns would just lead to the impressions being shared across them. This isn't inherently unproductive...
2) Bid staggering against yourself will make a difference but is influenced by what other advertisers are doing. If you bid $1.00, $0.90 and $0.80 and get similar volume but higher ROI from the $0.80 bid, chances are you were just bidding too high in the first place - the goal should be to just beat the highest other bidder.
If there is some competition, making duplicate campaigns with staggered bids allows you to find sweet spots of volume vs revenue/ROI. Being the highest bidder isn't always the most profitable position!
Thanks very much zeno for the very thorough explanation! I know what to do now. 
Amy
This sounds strange, because with exoclick I actually do like to compete with myself to get MORE traffic.
Let say I have very high CTR on 1 campain targetting one specific placement, i will just duplicate this campaign 10 times and get the same amount (approx) of impression for each but more in total.