I understand how you feel, did the same myself. Don't waste the time, the time could be used more wisely creating new sites. The best way I learned to increase adsense income is to add new websites "not fuss over 1". 1 site turned into 2, 2 into 3, and now I have 10, and the income from 10 un-optimizatized would beat the income from 1 super optimized.
Anything above 1.25% is good.
Also don't forget to take user intent into consideration. All niches have season "even if you think it does" and the season drives more clicks the non season. That season could be pay days, bonus days, weekends, etc. So some days "on season" your CTR can be 2.50%, but on off season it could be .90%.
So until you understand that the season or pattern of purchase, testing different placement is a waste of time. On on Season when they are ready to buy, people will hunt from you ads "unless they are below the fold".