Here is what I was told in 1969 at umpire school and when I went into the league. College coaches in soCal had already told me. Don’t call the high strike. That’s when we get home runs hit against us.
In the league the ump scout came around and told us squeeze the zone down and call the ball an inch or two outside.
My weakness, constancy on the low strike. We were supposed to do top off the knee, but most wanted us center knee.
Remember if you take the inside edge of the ball on the outside edge of the plate that makes the zone about 5 inches wider than the plate.