It is no easy as front is about +-20 degrees from the center.
And confirmed by my observations : front armor seem to be reachable when you move out of the frontal 45° (= 22.5° on each side of the tank)
90° would be more realistic imo because reaching side armour with a 22.5° angle virtualy quadruples the thickness of your armour.
How do you test that ?
Use a T64BV as target for exemple (cease fire) you need one of your units in cease fire mode in front of the target to prevent it from turningg (tanks face the closest ennemy) then use a tank that can penetrate the side armor of the T64 but not it's frontal armor. Move your shooter perpendicularly to the direction faced by the T64. When your unit start shooting (side armor can be reached) stop it, mesure the distances and calculate the angle using trigonometry.
Eugen's law of maximal pain in the ass : If anything can go wrong, it will go wrong on Friday evening.