Hydro - Ec stable, Ph dropping - Raise EC instead of lowering it ?

That is such a minor pH fluctuation I wouldn't worry about it. It is good to have some pH drift. You are using chelated nutrients, so a pH between 5.5-6.2 is completely fine. There is a study or two showing that 5.5 is optimal pH for yield etc, but that is another conversation. You are probably right about the cal-mag causing the pH drop. Calcium is a cation, so if it eats more cations than anions, the pH drops. Weeks 2-5 of flower they want the most food, so I would increase the EC and see how they handle it in your environment. Early flower they want calcium, P and always some K. Know that K is also a cation, so too much K will crash your pH as well. Those pH charts are ok, but I found it is much more complex then simply raising or lowering your EC.