Care to give more info?
Crosses from open play?
You can preempt by looking at the opposition players and set instructions before the match.
The delivery: marking, closing down, showing to a specific side. Do they come from deep, the byline?
The finisher: Is he big, slow, fast, nimble? Can you mark him out, do you have to drop off him?
The area it's played into: penalty spot, high at the far, the gap between the d-line and the keeper?
What side do you normally concede from? For instance your right side is weaker than your left.
Basically look to funnel attacks into your defensive strength. For instance I have work horses in the middle of the pitch with a holding player just in front of the defence, so my default instructions are to show players inside and congest the middle. If you have fast defenders, try to force the opponents to play balls that benefit your speed.
Crosses from set pieces?
You can look at this:
http://www.fm-base.co.uk/forum/share-download-fm-16-tactics/357742-corner-setup-compilation.html
An opposing set piece, unless perfectly executed, is a chance for a counter. They already have the players up, so most rational AI, unless chasing a narrow lead that has huge consequences (cup final, rivals, relegation, etc) will keep players back to prevent a counter. And if you build a reputation for countering, they will pull more back.
Why the BWM? Something that could be happening is your AP and BBM are up high, the BWM goes a chasing the ball, opposing player goes into space vacated by the BWM, CDs push up to close down and pressure that player, FBs don't cover or balance quick enough, and someone gets in behind to latch unto an early cross.