It's absolutely normal rating for these positions in FM15 and it doesn't depends on what tactic you use and it doesn't mean they do much worse than the rest of the team it's simple the ratings for these positions was coded that way this year FM.
"Swapping position" has no impact on the manual marking because it "marks" position and not the player so you shoudn't play attention to it.
After the sub manual marking alway stops working and you have to go the tactic menu and push "Confirmation" button to make it work again and if it didn't happen to you than you probably just messed up something.
Mate, I really don't think there's any "magic" trick which makes your strikers to score