Exchanging emails with a friend and a fellow Platoon addict we came to the same observation: In memories we’ve had of the movie, Barnes seemed to be towering above everyone else. But Tom Berenger is not that tall.
So I (again) took a look at the movie to examine which possible tricks could make us believe this. Well, some takes indeed suggest that Barnes is taller than others, but they are fewer than I assumed:
(click for bigger images)
Others just show him as he is…
Or even make him smaller… 
Those shots below CAN suggest size difference, in the first row it’s different camera angle, in the duelling scene Barnes’ face is placed slightly higher, and the last shot just uses perspective.
So it must have been the personality that makes us think Barnes was the biggest guy in the bunch… 
Spotted by the way: In this shot a black dressed figure is running through the field…
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