effects of position I have noticed in game: MC pushed forward did participated more in attacks. In one game tho was late to defend and got red.
DL and DR run box to box if placed even slightly forward, even on defensive mentality. good or bad, judge for yourself. if pushed back and as close to CD box they do not cross the centre except on rare CA here and there.
AML/R and ST I have NOT seen any obvious difference in action. it may only be prefered position when they are idle, really not limiting their behaviour.