Something like this (the 'Diff 32/8' means that the target difficulty is 8 and the submitted share had a difficulty of 32):
In your case with a speed of 24Ghps you may see a difficulty of 16. As for setting this yourself, no, currently that is not possible at BitMinter. It is automatically adjusted by the pool based on your hashrate.
How does the pool take into account the miner's higher difficulty set point that would correlate to a lower submitted hash rate and the payout share?