Strike zone questions

[gvsulife]

I have not had a lot of complaints because I have been calling this pitch a ball when the player is up in the box, but I had a kid really struggle the other night and it just made me start to think that maybe some of those pitches are strikes based upon the zone being at the plate not where the batter is. I am just trying to wrap my head around the concept and conversations I need to have with coaches to explain this and I wanted to get opinions from others.