Ok, as learnt and as suggested by others I was split testing my ads on content network in 1 adgroup but in another adgroup with similar kw just had 1 ad. The adgroup with 1 ad performed better over 3 week period with lower cpc than with adgroup with 2 ads. So I created 2 more adgroups with 1 ad each from 1st adgroup and boom both performed much better than having 2 ads in same adgroup. I learnt that for content network if you want to split test ads just create 1 adgroup per ad. Hope it helps, however the same theory does not apply for search.