Question: What is the safest defensive line for playing a Sweeper Keeper? Too deep and it's pointless, too high and it's dangerous. Anyone tested this?
This would be my advice, but bear in mind I've never used the corner exploit or even looked into there being one for fm2011:
I always make sure I have a center back at far post, and another challenging keeper. If you set your corners to 'far post' you will score maybe 1/10 corners with this setup. Alternatively aiming for near post and putting a talented header to 'near post flick on' (not attack near post) has good results, especially if you set a good finisher to attack the ball from deep (you'll either get a good headed goal from near post, or a player will run on from a deflection and knock one in).
These are my observations from playing with United in fm2011, for a couple of seasons. I always have Vidic/Brown attack far post (go forward for free kicks), Rio/Smalling challenge keeper (mark keeper with free kicks). I can see you've signed a few players so just choose the best heading player at your disposal for the near post flick on, and Rooney/Berbatov to attack from deep.
Worst comes to worst I always leave at least one midfielder to lurk outside the box (ahead of fullbacks), occasionally they knock one in no matter what tactic I use.
I definitely don't recommend 'Penalty Area' corners, as they very often drop to the other team and if you don't have enough players behind the ball, this leaves you very open.
I don't normally post advice (usually asking it, lol) so I hope this is vaguely helpful.