Data is moved based on access rate over time see whitepaper below, so if data becomes cold it may be demoted on the next scheduled move. The performance, balanced, cost settings just bias to the movement algorithm, you could also try adaptive flashcache to enable acceleration of data that's found itself in the wrong tier at the wrong time. But first have a look at the whitepaper to understand AO.
http://h20195.www2.hp.com/V2/GetPDF.asp ... 867ENW.pdfhttp://h20195.www2.hp.com/V2/GetPDF.asp ... 731ENW.pdf