Fiio's official spec says +4.2db at 100Hz , which I assume is what the newer batch does. Based on Fiio's graph, bass boost before 100 Hz should be even higher than +4.2 db.
However, Fiio's graph might not be updated to reflect batch 2 bass boost (it is contradictory to spec's +4.2db@100Hz). It shows a +2db@100Hz, which seems to be that of batch 1 bass boost.
ClieOS measured a batch 1 bass boost here and showed a graph similar to Fiio's: http://www.inearmatters.net/2013/03/impression-fiio-e12-mont-blanc-way-to.html?m=1
ClieOS also indicated that batch 2 bass boost will be broader and less deep/tight.