A few points for your reference:
1) Placing many players in a certain area (eg. STs, MCs, DCs) is reasonable to defend against or exploit weaknesses of certain formations, so it also makes sense to overload a certain flank too (eg. That opposition may have focused his resources into training several players to attack 1 flank, or simply his opposition has an extremely weak fullback [so it makes sense to keep attack focus there])
2) in a typical 4-5v-1 formation, both aml & AMR should have up-arrow to set their mentality as attacking; similarly, both fullbacks should also have down-arrow to concentrate on defending (it is much safer to minimise the chance of fullbacks going upfield and then concede counter attack goals by opponents wingers or wide midfielders); DCs & DMC could also have down-arrows (personal preference), while ST & MCs mostly would not use any arrows
3) Training first teamers with role or SA during a season is extremely damaging to player attributes improvement and chances of silverware.
An equivalent opponent who focuses on training key attributes would have seen some 20-30% improvement when you players gain nothing. So by the time of finals, you may have several players being able to play 1 more position, while your opposition have key white skills advantage of close to 30%. Needless to say, it is close to a definite loss against finals’ opponents who are most often the best.
Train SA or role at start of season using greens, or make use of the free one from special sponsor reward if any 1 player really needs a certain position flexibility.