Outside Corner

[canadaump6]

How does working the slot affect the view one has of the outside corner? Because I work the slot and have been very happy with my outside corner; anything that touches it I call a strike, even if only a fraction of the ball nicks it. But today a partner of mine told me I call pitches that are a foot and a half off the outside corner of the plate. This is scary and frustrating to me because although I am a bit more generous on the outside part of the plate, it is never nearly that bad. My rule of thumb is that if I see dirt between the ball and the black of the plate, it's not a strike. Apparently I am seeing things because what looks like a good pitch is actually a foot and a half off the plate. How does working the slot change the perception of the outside pitch?