What's your keepers stats like? Aerial Ability and Command Of Area are vital stats for defending corners & crossing!
Set you centre backs & full backs to Man Mark and Tight Marking this should reduce the amount of connected crosses...
Don't have your defensive line too deep as this allows their target man to get closer to your goal...
Defending corners, personally I have my full backs marking either post, have my centre backs marking tall players, all other players who are decent at heading are set to Go Back, the two most useless headers of the ball from my midfield and attack are left forward, I have someone close down the corner, and the rest is up to you....
Hope this helps?