Hi MKT…
1)One basic reason for diffrent tilts is, bcoz Electrical tilt is having less backlobe nd sidelobe as compared to mechanical tilt.
so in electrical tilt reduces the interference.
2)There is no such standard practise followed…but wat i have seen is that 2 deg of electrical is default.
3)values of tilt can be seen physically….for electrical tilt we had a nobe at the bottom of the antenna….nd mechanical tilt is given at the upper end of the antenna….where a clamp is move to adjaust the tilt.