Naw. Most likely you got the .01 for eCPM, and the two clicks were on PSA's which means 0 profit for you.
Yeah I definately think going full boar can hurt your overall earnings, depending on how deep your ad pool is. If you have all 4 ad positions, but you have only one or two high paid advertisers, chances are you will get a lot of lower paid ads and reduce earnings. This is not always the case though. If your particular target is deep with advertisers paying good money, you can place more ads and keep revenue up. Google is always going to place the best revenue generating ads first. This does not always mean the highest payout per click, but is a combination of payout with click rate. The more ads you have, the greater chance you have of providing reduced value options to your visitors. I would guess this is even more prevelent if you have multiple advertisers in very similar niches where a visitor is likely to choose either one.. Although I think some of the new changes to Adwords makes it so similar ads are likely to yield similar payouts.
Is it when PSA ads is showing mean there is not enough pools of advertisers, and thus better to reduce amount of ads?
Could be, or it might be that the page isn't optimized right, so Googlebot is getting the wrong information about what the page is all about. Setting up each page correctly is very important.
1 cents, and worse, less than 1 cents click coming back! Any way to chase it away? How to identify which ads is it?
Based on what I have read about adsense, the ads on top page should pay higher than the bottom page. so put the big rectangle of adsense at the top page and if you want, u can also put banner at the bottom. Those who have website, u can combine with other ads such as kontera or even affiliate program from commission junction & clickbank. I only add it to my site yesterday and waiting to see the performance of each type of ads. See the sample at cash2catch dot com
do not use too many ads !! do not make them annoying users are humans, they prefer website in which ads do not disturb browsing. If number of ads is too big or or ad placement is too evident, users woun't click on ads and will leave it imediantly, except if your site contains valuable resourses.