Because I hate people who espouse 'fact' without proof. Screen used armour on a different body type, camera angle, lighting , version of suit, first, second, or third tier of suit quality made for the movie...all cause differences. If a suit was scanned with roto cameras it will be different then a flat 3d scanner. If a suit made for close ups and good lighting was use vs a suit used for background shots, bad lights, that was produced to wider tolerances, different results. Both are screen origin.
Unless someone worked on set and has proper images next to his anovos suit...