wah the how you control your SS and EV?
Say i wanna have less DOF for more bokeh, and i choose to use f2. If the shutter speed calculated by the camera still isnt fast enough for what i am shooting, then i bump up my iso till i get the shutter speed that i want. For EV in A mode its calculated for you ma, can make use of the EV compensation to get what you want. When shooting bright colours like white + EV, when shooting dark colours like black -EV