To clarify ( after a lot of talks here in the forum and with the support ) , AML and AMR very high are not playing like MC but is a legit role , They are playing in the Second Striker role, a role between AMC and ST , to understand look this pic
The role is also called "central winger", cause they are wingers that play in the middle instead of the flanks
Regarding the arrows , i did a lot of tests ( and also a lot of talks about it )and in some roles you can see your player play in a more foward postition or
in a more deeper position , if you want to see it do this easy test : play a match with a defensive mentality and with a formation with MR (or ML ) and change the arrow on him during the match , you will see ( in the animation ) the player starting position more up or more deep.
Like i said before i can see the effect more on flank roles, amc and dmc role too , st sometimes ( with a back arrows sometimes drop deeper ) , difficult to see the effect on MC's (cause they already have the duty to go up and down) , DC difficult to see the effect.
So arrows simply make your player play in a more foward position or in a more deeper position than his starting position.