Yes, you should definitively soften the 60%. First, I think there are only very few bonus combinations where hard mode is currently beatable. Second, it will be more fun, not because of the reduced frustration but because you have more decisions to make.
My suggestion is 70%. On a station with 3 officers available, the probability of getting at least two missions is 78.4%, having only one mission 18.9%, and having no mission at all 2.7% (compared to 64.8%, 28.8%, and 6.4%). This is, about on 4 of 5 days, you have to make a decision.
I'm looking forward to whatever decision you make.