I've been experimenting a little with arrows.

First defenders.
Previously only ever put down arrows on the centre DC of three, to act as a sweeper against two strikers, or up arrows on DL/DR when playing the V formation.

For the last few days I've put them on all three, with different mentality settings and counter options.
When used with defensive mentality no counter they definitely do not venture to far up field, which is what you want.
In attacking mentality with off side on they moved forward but seem to drop to deep when out of possession, my MF and DM's seem to be doing far more tackling which IMO accounted for 4 bookings in two games.
In normal with no off side and no counter they were all over the place scoring from open play.

So while I'm still not 100% that arrows do a great deal I will persist wit the trials, the same goes for AM's and ST I'm not convinced they do a great deal.

My reasoning is that you cannot rely on the game engine to be giving a true picture of where players are and what they are actually doing.
There's is only one constant on Tll, inconsistency! there lies the problem, utter confusion.