bq40z50 high current application

I'm attempting to use a bq40z50 in a high current application (2-3C discharge). I did the IT calibration as described, with a C/5 discharge, and the gauge seems to be tracking capacity well at low rates of charge/discharge. However, when I try to discharge at 3C, the 'true' capacity measurement drops mid way through discharge (from say 70% to 0%) even though the battery still has approx 70% charge remaining. The 'float' capacity measurement moves more slowly.

Is there a configuration I should set to make the gauge perform better? Should I do the IT calibration process differently?

Thanks,

Ben