When your effort is all on hitting the ball back you often give a larger margin of error because you aren't concentrating on exactly where the ball lands. This is why people will often play a ball that is out by an inch or two when they are trying to hit the ball still.
On the other hand when you have given up on hitting the ball and just watch to see if it lands in or out you can be more precise as all your concentration is focused on just seeing if the ball landed in or out.
SO be grateful that you have been getting some "benefit of the doubt" calls when your ball is only an inch out, rather than being angry when they actually call it.
Völkl PB10 Mid / Pro's Pro Hi-Tec Multifiber 1.30mm @ 55lbs